Ceramic materials, abrasive particles, abrasive articles, and methods of making and using the same

ABSTRACT

Amorphous materials, glass-ceramics and methods of making the same. Embodiments of the invention include abrasive particles. The abrasive particles can be incorporated into a variety of abrasive articles, including bonded abrasives, coated abrasives, nonwoven abrasives, and abrasive brushes.

[0001] This application is a continuation-in-part of U.S. Ser. Nos.09/922,526, 09/922,527, 09/922,528, and 09/922,530, filed Aug. 2, 2001,the disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates to amorphous materials and glass-ceramics.In another aspect, embodiments of the present invention relates toabrasive particles and abrasive articles incorporating the abrasiveparticles therein.

DESCRIPTION OF RELATED ART

[0003] A large number of amorphous (including) glass and glass-ceramiccompositions are known. The majority of oxide glass systems utilizewell-known glass-formers such as SiO₂, B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃,and V₂O₅ to aid in the formation of the glass. Some of the glasscompositions formed with these glass-formers can be heat-treated to formglass-ceramics. The upper use temperature of glasses and glass-ceramicsformed from such glass formers is generally less than 1200° C.,typically about 700-800° C. The glass-ceramics tend to be moretemperature resistant than the glass from which they are formed.

[0004] In addition, many properties of known glasses and glass-ceramicsare limited by the intrinsic properties of glass-formers. For example,for SiO₂, B₂O₃, and P₂O₅-based glasses and glass-ceramics, the Young'smodulus, hardness, and strength are limited by such glass-formers. Suchglass and glass-ceramics generally have inferior mechanical propertiesas compared, for example, to Al₂O₃ or ZrO₂. Glass-ceramics having anymechanical properties similar to that of Al₂O₃ or ZrO₂ would bedesirable.

[0005] Although some non-conventional glasses such as glasses based onrare earth oxide-aluminum oxide (see, e.g., PCT application havingpublication No. WO 01/27046 A1, published Apr. 19, 2001, and JapaneseDocument No. JP 2000-045129, published Feb. 15, 2000) are known,additional novel glasses and glass-ceramic, as well as use for bothknown and novel glasses and glass-ceramics is desired.

[0006] In another aspect, a variety of abrasive particles (e.g., diamondparticles, cubic boron nitride particles, fused abrasive particles, andsintered, ceramic abrasive particles (including sol-gel-derived abrasiveparticles) known in the art. In some abrading applications, the abrasiveparticles are used in loose form, while in others the particles areincorporated into abrasive products (e.g., coated abrasive products,bonded abrasive products, non-woven abrasive products, and abrasivebrushes). Criteria used in selecting abrasive particles used for aparticular abrading application include: abrading life, rate of cut,substrate surface finish, grinding efficiency, and product cost.

[0007] From about 1900 to about the mid-1980's, the premier abrasiveparticles for abrading applications such as those utilizing coated andbonded abrasive products were typically fused abrasive particles. Thereare two general types of fused abrasive particles: (1) fused alphaalumina abrasive particles (see, e.g., U.S. Pat. No. 1,161,620(Coulter), U.S. Pat. No. 1,192,709 (Tone), U.S. Pat. No. 1,247,337(Saunders et al.), U.S. Pat. No. 1,268,533 (Allen), and U.S. Pat. No.2,424,645 (Baumann et al.)) and (2) fused (sometimes also referred to as“co-fused”) alumina-zirconia abrasive particles (see, e.g., U.S. Pat.No. 3,891,408 (Rowse et al.), U.S. Pat. No. 3,781,172 (Pett et al.),U.S. Pat. No. 3,893,826 (Quinan et al.), U.S. Pat. No. 4,126,429(Watson), U.S. Pat. No. 4,457,767 (Poon et al.), and U.S. Pat. No.5,143,522 (Gibson et al.))(also see, e.g., U.S. Pat. No. 5,023,212(Dubots et. al) and U.S. Pat. No. 5,336,280 (Dubots et. al) which reportthe certain fused oxynitride abrasive particles). Fused alumina abrasiveparticles are typically made by charging a furnace with an aluminasource such as aluminum ore or bauxite, as well as other desiredadditives, heating the material above its melting point, cooling themelt to provide a solidified mass, crushing the solidified mass intoparticles, and then screening and grading the particles to provide thedesired abrasive particle size distribution. Fused alumina-zirconiaabrasive particles are typically made in a similar manner, except thefurnace is charged with both an alumina source and a zirconia source,and the melt is more rapidly cooled than the melt used to make fusedalumina abrasive particles. For fused alumina-zirconia abrasiveparticles, the amount of alumina source is typically about 50-80 percentby weight, and the amount of zirconia, 50-20 percent by weight zirconia.The processes for making the fused alumina and fused alumina abrasiveparticles may include removal of impurities from the melt prior to thecooling step.

[0008] Although fused alpha alumina abrasive particles and fusedalumina-zirconia abrasive particles are still widely used in abradingapplications (including those utilizing coated and bonded abrasiveproducts, the premier abrasive particles for many abrading applicationssince about the mid-1980's are sol-gel-derived alpha alumina particles(see, e.g., U.S. Pat. No. 4,314,827 (Leitheiser et al.), U.S. Pat. No.4,518,397 (Leitheiser et al.), U.S. Pat. No. 4,623,364 (Cottringer etal.), U.S. Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671(Monroe et al.), U.S. Pat. No. 4,881,951 (Wood et al.), U.S. Pat. No.4,960,441 (Pellow et al.), U.S. Pat. No. 5,139,978 (Wood), U.S. Pat. No.5,201,916 (Berg et al.), U.S. Pat. No. 5,366,523 (Rowenhorst et al.),U.S. Pat. No. 5,429,647 (Larmie), U.S. Pat. No. 5,547,479 (Conwell etal.), U.S. Pat. No. 5,498,269 (Larmie), U.S. Pat. No. 5,551,963(Larmie), and U.S. Pat. No. 5,725,162 (Garg et al.)).

[0009] The sol-gel-derived alpha alumina abrasive particles may have amicrostructure made up of very fine alpha alumina crystallites, with orwithout the presence of secondary phases added. The grinding performanceof the sol-gel derived abrasive particles on metal, as measured, forexample, by life of abrasive products made with the abrasive particleswas dramatically longer than such products made from conventional fusedalumina abrasive particles.

[0010] Typically, the processes for making sol-gel-derived abrasiveparticles are more complicated and expensive than the processes formaking conventional fused abrasive particles. In general,sol-gel-derived abrasive particles are typically made by preparing adispersion or sol comprising water, alumina monohydrate (boehmite), andoptionally peptizing agent (e.g., an acid such as nitric acid), gellingthe dispersion, drying the gelled dispersion, crushing the drieddispersion into particles, screening the particles to provide thedesired sized particles, calcining the particles to remove volatiles,sintering the calcined particles at a temperature below the meltingpoint of alumina, and screening and grading the particles to provide thedesired abrasive particle size distribution. Frequently a metal oxidemodifier(s) is incorporated into the sintered abrasive particles toalter or otherwise modify the physical properties and/or microstructureof the sintered abrasive particles.

[0011] There are a variety of abrasive products (also referred to“abrasive articles”) known in the art. Typically, abrasive productsinclude binder and abrasive particles secured within the abrasiveproduct by the binder. Examples of abrasive products include: coatedabrasive products, bonded abrasive products, nonwoven abrasive products,and abrasive brushes.

[0012] Examples of bonded abrasive products include: grinding wheels,cutoff wheels, and honing stones. The main types of bonding systems usedto make bonded abrasive products are: resinoid, vitrified, and metal.Resinoid bonded abrasives utilize an organic binder system (e.g.,phenolic binder systems) to bond the abrasive particles together to formthe shaped mass (see, e.g., U.S. Pat. No. 4,741,743 (Narayanan et al.),U.S. Pat. No. 4,800,685 (Haynes et al.), U.S. Pat. No. 5,037,453(Narayanan et al.), and U.S. Pat. No. 5,110,332 (Narayanan et al.)).Another major type are vitrified wheels in which a glass binder systemis used to bond the abrasive particles together mass (see, e.g., U.S.Pat. No. 4,543,107 (Rue), U.S. Pat. No. 4,898,587 (Hay et al.), U.S.Pat. No. 4,997,461 (Markhoff-Matheny et al.), and U.S. Pat. No.5,863,308 (Qi et al.)). These glass bonds are usually matured attemperatures between 900° C. to 1300° C. Today vitrified wheels utilizeboth fused alumina and sol-gel-derived abrasive particles. However,fused alumina-zirconia is generally not incorporated into vitrifiedwheels due in part to the thermal stability of alumina-zirconia. At theelevated temperatures at which the glass bonds are matured, the physicalproperties of alumina-zirconia degrade, leading to a significantdecrease in their abrading performance. Metal bonded abrasive productstypically utilize sintered or plated metal to bond the abrasiveparticles.

[0013] The abrasive industry continues to desire abrasive particles andabrasive products that are easier to make, cheaper to make, and/orprovide performance advantage(s) over conventional abrasive particlesand products.

SUMMARY OF THE INVENTION

[0014] In one aspect, the present invention provides amorphous materialcomprising at least 35 (in some embodiments, preferably at least 40, 45,50, 55, 60, 65, or even at least 70) percent by weight Al₂O₃, based onthe total weight of the amorphous material, and a metal oxide other thanAl₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, andcomplex metal oxides thereof), wherein the amorphous material containsnot more than 10 (in some embodiments preferably, less than 5, 4, 3, 2,1, or even zero) percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅,SiO₂, TeO₂, and V₂O₅, based on the total weight of the amorphousmaterial, wherein the amorphous material has x, y, and z dimensions eachperpendicular to each other, and wherein each of the x, y, and zdimensions is at least 5 mm (in some embodiments, at least 10 mm).Optionally, the amorphous material is heat-treated such that at least aportion of the amorphous material is converted to a glass-ceramic.

[0015] The x, y, and z dimensions of a material are determined eithervisually or using microscopy, depending on the magnitude of thedimensions. The reported z dimension is, for example, the diameter of asphere, the thickness of a coating, or the longest length of a prismaticshape.

[0016] In one aspect, the present invention provides amorphous materialcomprising at least 35 (in some embodiments, preferably at least 40, 45,50, 55, 60, 65, or even at least 70) percent by weight Al₂O₃, based onthe total weight of the amorphous material, and a metal oxide other thanAl₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, andcomplex metal oxides thereof), wherein the amorphous material containsnot more than 10 (in some embodiments preferably, less than 5, 4, 3, 2,1, or even zero) percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅,SiO₂, TeO₂, and V₂O₅, based on the total weight of the amorphousmaterial, with the proviso that if the metal oxide other than Al₂O₃ isCaO or ZrO₂, then the amorphous material further comprises a metal oxideother than Al₂O₃, CaO, and ZrO₂ at least a portion of which forms adistinct crystalline phase when the amorphous material is crystallized.In some embodiments, the amorphous material has x, y, and z dimensionseach perpendicular to each other, and wherein each of the x, y, and zdimensions is at least 5 mm (in some embodiments, at least 10 mm).Optionally, the amorphous material is heat-treated such that at least aportion of the amorphous material is converted to a glass-ceramic.

[0017] A “distinct crystalline phase” is a crystalline phase that isdetectable by x-ray diffraction as opposed to a phase that is present insolid solution with another distinct crystalline phase. For example, itis well known that oxides such as Y₂O₃ or CeO₂ may be in solid solutionwith a crystalline ZrO₂ and serve as a phase stabilizer. The Y₂O₃ orCeO₂ in such instances is not a distinct crystalline phase.

[0018] In some embodiments, the amorphous material comprises 0 to 70, 0to 50, 0 to 25, or even 0 to 10 percent by weight of the metal oxideother than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO,CuO, and complex metal oxides thereof), and/or 0 to 50, 0 to 25, or even0 to 10 percent by weight of at least one of ZrO₂ or HfO₂, based on thetotal weight of the amorphous material.

[0019] In some embodiments, the amorphous material may present inanother material (e.g., particles comprising the amorphous materialaccording to the present invention, ceramic comprising the amorphousmaterial according to the present invention, etc.). Optionally, theamorphous material (including a glass) is heat-treated such at least aportion of the amorphous material is converted to a glass-ceramic.

[0020] In another aspect, the present invention provides glasscomprising at least 35 (in some embodiments, preferably at least 40, 45,50, 55, 60, 65, or even at least 70) percent by weight Al₂O₃, based onthe total weight of the glass, and a metal oxide other than Al₂O₃ (e.g.,Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, and complex metaloxides thereof), wherein the glass contains not more than 10 (in someembodiments preferably, less than 5 or even zero) percent by weightcollectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of the glass, wherein the glass has x, y, and z dimensionseach perpendicular to each other, and wherein each of the x, y, and zdimensions is at least at least 5 mm (in some embodiments, at least 10mm). In some embodiments, the glass may present in another material(e.g., particles comprising the glass according to the presentinvention, ceramic comprising the glass according to the presentinvention, etc.). Optionally, the glass is heat-treated such that atleast a portion of the glass is converted to a glass-ceramic.

[0021] In another aspect, the present invention provides glasscomprising at least 35 (in some embodiments, preferably at least 40, 45,50, 55, 60, 65, or even at least 70) percent by weight Al₂O₃, based onthe total weight of the glass, and a metal oxide other than Al₂O₃ (e.g.,Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, and complex metaloxides thereof), wherein the glass contains not more than 10 (in someembodiments preferably, less than 5 or even zero) percent by weightcollectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of the glass, with the proviso that if the metal oxideother than Al₂O₃ is CaO, then the glass further comprises a metal oxideother than Al₂O₃ or CaO at least a portion of which forms a distinctcrystalline phase when the glass is crystallized. In some embodiments,the glass has x, y, and z dimensions each perpendicular to each other,and wherein each of the x, y, and z dimensions is at least at least 5 mm(in some embodiments, at least 10 mm). In some embodiments, the glassmay present in another material (e.g., particles comprising the glassaccording to the present invention, ceramic comprising the glassaccording to the present invention, etc.). Optionally, the glass isheat-treated such that at least a portion of the glass is converted to aglass-ceramic.

[0022] In some embodiments, the glass comprises 0 to 70, 0 to 50, 0 to25, or even 0 to 10 percent by weight of the metal oxide other thanAl₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, andcomplex metal oxides thereof), and/or 0 to 50, 0 to 25, or even 0 to 10percent by weight of at least one of ZrO₂ or HfO₂, based on the totalweight of the glass.

[0023] In another aspect, the present invention provides a method formaking an article comprising glass comprising at least 35 (in someembodiments, preferably at least 40, 45, 50, 55, 60, 65, or even atleast 70) percent by weight Al₂O₃, based on the total weight of theglass, and a metal oxide other than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂,CaO, Cr₂O₃, MgO, NiO, CuO, and complex metal oxides thereof), whereinthe glass contains not more than 10 (in some embodiments preferably,less than 5, 4, 3, 2, 1, or even zero) percent by weight collectivelyAs₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, P₂O₅, TeO₂, and V₂O₅, based on the totalweight of the glass, the method comprising:

[0024] providing glass particles comprising at least 35 (in someembodiments, preferably at least 40, 45, 50, 55, 60, 65, or even atleast 70) percent by weight Al₂O₃, based on the total weight of theglass, and a metal oxide other than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂,CaO, Cr₂O₃, MgO, NiO, CuO, and complex metal oxides thereof), whereinthe glass contains not more than 10 (in some embodiments preferably,less than 5, 4, 3, 2, 1, or even zero) percent by weight As₂O₃, B₂O₃,GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theglass, the glass having a T_(g);

[0025] heating the glass particles above the T_(g) such that the glassparticles coalesce to form a shape; and

[0026] cooling the shape to provide the article, with the proviso thatif the metal oxide other than Al₂O₃ is CaO or ZrO₂, then the glassfurther comprises a metal oxide other than Al₂O₃ or CaO at least aportion of which forms a distinct crystalline phase when the glass iscrystallized. Optionally, glass comprising the article is heat-treatedsuch that at least a portion of the glass is converted to aglass-ceramic. In some embodiments, the glass and glass-ceramic comprise0 to 70, 0 to 50, 0 to 25, or even 0 to 10 percent by weight of themetal oxide other than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃,MgO, NiO, CuO, and complex metal oxides thereof), and/or 0 to 50, 0 to25, or even 0 to 10 percent by weight of at least one of ZrO₂ or HfO₂,based on the total weight of the glass and glass-ceramic, respectively.

[0027] In another aspect, the present invention provides a method formaking glass particles, the method comprising:

[0028] atomizing a glass melt comprising at least 35 (in someembodiments, preferably at least 40, 45, 50, 55, 60, 65, or even atleast 70) percent by weight Al₂O₃, based on the total weight of theglass melt, and a metal oxide other than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂,TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, and complex metal oxides thereof),wherein the glass melt contains not more than 10 (in some embodimentspreferably, less than 5 or even zero) percent by weight collectivelyAs₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weightof the glass melt; and

[0029] cooling the atomized glass melt to provide glass particlescomprising at least 35 (in some embodiments, preferably at least 40, 45,50, 55, 60, 65, or even at least 70) percent by weight Al₂O₃, based onthe total weight of each glass particle, and a metal oxide other thanAl₂O₃, wherein each glass particle contains not more than 10 (in someembodiments preferably, less than 5 or even zero) percent by weightcollectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of each glass particle, wherein the glass has x, y, and zdimensions each perpendicular to each other, and wherein each of the x,y, and z dimensions is at least 5 mm (in some embodiments, at least 10mm), with the proviso that if the metal oxide other than Al₂O₃ is CaO orZrO₂, then the glass further comprises a metal oxide other than Al₂O₃ orCaO at least a portion of which at least a portion of which forms adistinct crystalline phase when the glass is crystallized. Optionally,the glass is heat-treated such that at least a portion of the glass isconverted to a glass-ceramic. In some embodiments, the glass andglass-ceramic comprise 0 to 50, 0 to 25, or even 0 to 10 percent byweight of the metal oxide other than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂,CaO, Cr₂O₃, MgO, NiO, CuO, and complex metal oxides thereof), and/or 0to 50, 0 to 25, or even 0 to 10 percent by weight of at least one ofZrO₂ or HfO₂, based on the total weight of the glass and glass-ceramic,respectively.

[0030] In another aspect, the present invention provides a glass-ceramiccomprising at least 35 (in some embodiments, preferably at least 40, 45,50, 55, 60, 65, or even at least 70) percent by weight Al₂O₃, based onthe total weight of the glass-ceramic, and a metal oxide other thanAl₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, andcomplex metal oxides thereof), wherein the glass-ceramic contains notmore than 10 (in some embodiments preferably, less than 5, 4, 3, 2, 1,or even zero) percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅,SiO₂, TeO₂, and V₂O₅, based on the total weight of the glass-ceramic,wherein the glass-ceramic has x, y, and z dimensions each perpendicularto each other, and wherein each of the x, y, and z dimensions is atleast 5 mm (in some embodiments, at least 10 mm), with the proviso thatif the metal oxide other than Al₂O₃ is CaO, then the glass-ceramicfurther comprises crystals of a metal oxide other than CaO. In someembodiments, the glass-ceramic may present in another material (e.g.,particles comprising the glass-ceramic according to the presentinvention, ceramic comprising the glass-ceramic according to the presentinvention, etc.). In some embodiments, the glass-ceramic comprises 0 to50, 0 to 25, or even 0 to 10 percent by weight of the metal oxide otherthan Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, andcomplex metal oxides thereof), and/or 0 to 50, 0 to 25, or even 0 to 10percent by weight of at least one of ZrO₂ or HfO₂, based on the totalweight of the glass-ceramic.

[0031] In another aspect, the present invention provides a method formaking glass-ceramic, the method comprising heat-treating amorphousmaterial (including glass) according to the present invention such thatat least a portion of the amorphous material is converted to aglass-ceramic.

[0032] In another aspect, the present invention provides a method formaking abrasive particles, the method comprising:

[0033] heat-treating amorphous material (including a glass) according tothe present invention such that at least a portion of the amorphousmaterial is converted to a glass-ceramic; and

[0034] crushing the glass-ceramic to provide abrasive particlescomprising the glass-ceramic.

[0035] The abrasive particles can be incorporated into an abrasivearticle, or used in loose form. Abrasive articles according to thepresent invention comprise binder and a plurality of abrasive particles,wherein at least a portion of the abrasive particles are the abrasiveparticles according to the present invention. Exemplary abrasiveproducts include coated abrasive articles, bonded abrasive articles(e.g., wheels), non-woven abrasive articles, and abrasive brushes.Coated abrasive articles typically comprise a backing having first andsecond, opposed major surfaces, and wherein the binder and the pluralityof abrasive particles form an abrasive layer on at least a portion ofthe first major surface.

[0036] In some embodiments, preferably, at least 5, 10, 15, 20, 25, 30,35, 40, 45, 50 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100 percentby weight of the abrasive particles in an abrasive article are theabrasive particles according to the present invention, based on thetotal weight of the abrasive particles in the abrasive article.

[0037] Abrasive particles are usually graded to a given particle sizedistribution before use. Such distributions typically have a range ofparticle sizes, from coarse particles fine particles. In the abrasiveart this range is sometimes referred to as a “coarse”, “control” and“fine” fractions. Abrasive particles graded according to industryaccepted grading standards specify the particle size distribution foreach nominal grade within numerical limits. Such industry acceptedgrading standards (i.e., specified nominal grades) include those knownas the American National Standards Institute, Inc. (ANSI) standards,Federation of European Producers of Abrasive Products (FEPA) standards,and Japanese Industrial Standard (JIS) standards. In one aspect, thepresent invention provides a plurality of abrasive particles having aspecified nominal grade, wherein at least a portion of the plurality ofabrasive particles are abrasive particles according to the presentinvention. In some embodiments, preferably, at least 5, 10, 15, 20, 25,30, 35, 40, 45, 50 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100percent by weight of the plurality of abrasive particles are theabrasive particles according to the present invention, based on thetotal weight of the plurality of abrasive particles.

[0038] In another aspect, the present invention provides a method formaking abrasive particles according to the present invention, the methodcomprising heat-treating particles comprising the amorphous material(including glass) according to the present invention such that at leasta portion of the amorphous material converts to a glass-ceramic providethe abrasive particles comprising the glass-ceramic. Typically, theabrasive particles comprising the glass-ceramic are graded afterheat-treating to provide a plurality of abrasive particles having aspecified nominal grade, wherein at least a portion of the plurality ofabrasive particles is a plurality of the abrasive particles comprisingthe glass-ceramic. Optionally, prior to the heat-treating the particlesthe amorphous material, a plurality of particles having a specifiednominal grade is provided, wherein at least a portion of the particlesis a plurality of the particles comprising the amorphous material to beheat-treated, and wherein the heat-treating is conducted such that aplurality of abrasive particles having a specified nominal grade isprovided, wherein at least a portion of the abrasive particles is aplurality of the abrasive particles comprising the glass-ceramic.

[0039] In another aspect, the present invention provides a method formaking abrasive particles according to the present invention, the methodcomprising heat-treating particles comprising the amorphous materialsuch that at least a portion of the amorphous material converts to aglass-ceramic to provide the abrasive particles comprising theglass-ceramic. Typically, the abrasive particles comprising theglass-ceramic are graded after heat-treating to provide a plurality ofabrasive particles having a specified nominal grade, wherein at least aportion of the plurality of abrasive particles is a plurality of theabrasive particles comprising the glass-ceramic. Optionally, prior tothe heat-treating the particles comprising the amorphous material, aplurality of particles having a specified nominal grade is provided,wherein at least a portion of the particles is a plurality of theparticles comprising the amorphous material to be heat-treated, andwherein the heat-treating is conducted such that a plurality of abrasiveparticles having a specified nominal grade is provided, wherein at leasta portion of the abrasive particles is a plurality of the abrasiveparticles comprising the glass-ceramic.

[0040] In another aspect, the present invention provides a plurality ofabrasive particles having a specified nominal grade, wherein at least aportion of the abrasive particles is a plurality of abrasive particlescomprising a glass-ceramic, the glass-ceramic comprising at least 35 (insome embodiments, preferably at least 40, 45, 50, 55, 60, 65, or even atleast 70) percent by weight Al₂O₃, based on the total weight of theglass-ceramic of each particle of the portion, and a metal oxide otherthan Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, andcomplex metal oxides thereof), wherein the glass-ceramic contains notmore than 10 (in some embodiments preferably, less than 5, 4, 3, 2, 1,or even zero) percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅,SiO₂, TeO₂, and V₂O₅, based on the total weight of the glass-ceramic ofeach particle of the portion. In some embodiments, the glass-ceramiccomprise 0 to 50, 0 to 25, or even 0 to 10 percent by weight of themetal oxide other than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃,MgO, NiO, CuO, and complex metal oxides thereof), and/or 0 to 50, 0 to25, or even 0 to 10 percent by weight of at least one of ZrO₂ or HfO₂,based on the total weight of the glass-ceramic. In some embodiments, theglass-ceramic has x, y, and z dimensions each perpendicular to eachother, and wherein each of the x, y, and z dimensions is at least 25micrometers, 30 micrometers, 35 micrometers, 40 micrometers, 45micrometers, 50 micrometers, 75 micrometers, 100 micrometers, 150micrometers, 200 micrometers, 250 micrometers, 500 micrometers, 1000micrometers, 2000 micrometers, 2500 micrometers, 1 mm, 5 mm, or even atleast 10 mm. In some embodiments, if the metal oxide other than Al₂O₃ isCaO, then the glass-ceramic further comprises at least one distinctcrystalline phase of a metal oxide other than CaO. In some embodiments,if the metal oxide other than Al₂O₃ is ZrO₂, then the glass-ceramicfurther comprises at least one distinct crystalline phase of a metaloxide other than ZrO₂. In some embodiments, if the metal oxide otherthan Al₂O₃ is CaO or ZrO₂, then the glass-ceramic further comprises atleast one distinct crystalline phase of a metal oxide other than CaO orZrO₂.

[0041] In another aspect, the present invention provides a method formaking abrasive particles, the method comprising:

[0042] providing a plurality of particles having a specified nominalgrade, wherein at least a portion of the particles is a plurality ofparticles comprising an amorphous material, the amorphous materialcomprising at least 35 (in some embodiments, preferably at least 40, 45,50, 55, 60, 65, or even at least 70) percent by weight Al₂O₃, based onthe total weight of the amorphous material of each particle of theportion, and a metal oxide other than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂,TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, and complex metal oxides thereof),wherein the amorphous material contains not more than 10 (in someembodiments preferably, less than 5 or even zero) percent by weightcollectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of the amorphous material of each particle of the portion;and

[0043] heat-treating the particles comprising the amorphous materialsuch that at least a portion of the amorphous material is converted to aglass-ceramic and such that a plurality of abrasive particles having aspecified nominal grade is provided, wherein at least a portion of theabrasive particles is a plurality of abrasive particles comprising theglass-ceramic. In some embodiments, the glass and glass-ceramic comprise0 to 50, 0 to 25, or even 0 to 10 percent by weight of the metal oxideother than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO,CuO, and complex metal oxides thereof), and/or 0 to 50, 0 to 25, or even0 to 10 percent by weight of at least one of ZrO₂ or HfO₂, based on thetotal weight of the glass and glass-ceramic, respectively.

[0044] In another aspect, the present invention provides a method formaking abrasive particles, the method comprising:

[0045] heat-treating particles comprising an amorphous material suchthat at least a portion of the glass is converted to a glass-ceramic,the amorphous material comprising at least 35 (in some embodiments,preferably at least 40, 45, 50, 55, 60, 65, or even at least 70) percentby weight Al₂O₃, based on the total weight of the amorphous material ofeach particle of the portion, and a metal oxide other than Al₂O₃ (e.g.,Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, and complex metaloxides thereof), wherein the amorphous material contains not more than10 (in some embodiments preferably, less than 5 or even zero) percent byweight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, basedon the total weight of the amorphous material of each particle; and

[0046] grading the abrasive particles comprising the glass-ceramic toprovide a plurality of abrasive particles having a specified nominalgrade, wherein at least a portion of the plurality of abrasive particlesis a plurality of the abrasive particles comprising the glass-ceramic.In some embodiments, the glass and glass-ceramic comprise 0 to 50, 0 to25, or even 0 to 10 percent by weight of the metal oxide other thanAl₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, andcomplex metal oxides thereof), and/or 0 to 50, 0 to 25, or even 0 to 10percent by weight of at least one of ZrO₂ or HfO₂, based on the totalweight of the glass and glass-ceramic, respectively.

[0047] In another aspect, the present invention provides a method formaking abrasive particles, the method comprising:

[0048] heat-treating amorphous material such that at least a portion ofthe amorphous material is converted to a glass-ceramic, the amorphousmaterial comprising at least 35 (in some embodiments, preferably atleast 40, 45, 50, 55, 60, 65, or even at least 70) percent by weightAl₂O₃, based on the total weight of the amorphous material, and a metaloxide other than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO,NiO, CuO, and complex metal oxides thereof), wherein the amorphousmaterial contains not more than 10 (in some embodiments preferably, lessthan 5 or even zero) percent by weight collectively As₂O₃, B₂O₃, GeO₂,P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of the amorphousmaterial;

[0049] crushing the glass-ceramic to provide abrasive particlescomprising the glass-ceramic; and

[0050] grading the abrasive particles comprising the glass-ceramic toprovide a plurality of abrasive particles having a specified nominalgrade, wherein at least a portion of the plurality of abrasive particlesis a plurality of the abrasive particles comprising the glass-ceramic.In some embodiments, the glass and glass-ceramic comprise 0 to 50, 0 to25, or even 0 to 10 percent by weight of the metal oxide other thanAl₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, andcomplex metal oxides thereof), and/or 0 to 50, 0 to 25, or even 0 to 10percent by weight of at least one of ZrO₂ or HfO₂, based on the totalweight of the glass and glass-ceramic, respectively.

[0051] In another aspect, the present invention provides a method formaking abrasive particles, the method comprising:

[0052] heat-treating ceramic comprising an amorphous material such thatat least a portion of the amorphous material is converted to aglass-ceramic, the amorphous material comprising at least 35 (in someembodiments, preferably at least 40, 45, 50, 55, 60, 65, or even atleast 70) percent by weight Al₂O₃, based on the total weight of theamorphous material, and a metal oxide other than Al₂O₃ (e.g., Y₂O₃, REO,ZrO₂, Ti₂, CaO, Cr₂O₃, MgO, NiO, CuO, and complex metal oxides thereof),wherein the amorphous material contains not more than 10 (in someembodiments preferably, less than 5 or even zero) percent by weightcollectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of the amorphous material;

[0053] crushing the glass-ceramic to provide abrasive particlescomprising the glass-ceramic; and

[0054] grading the abrasive particles comprising the glass-ceramic toprovide a plurality of abrasive particles having a specified nominalgrade, wherein at least a portion of the plurality of abrasive particlesis a plurality of the abrasive particles comprising the glass-ceramic.In some embodiments, the glass and glass-ceramic comprise 0 to 50, 0 to25, or even 0 to 10 percent by weight of the metal oxide other thanAl₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, andcomplex metal oxides thereof), and/or 0 to 50, 0 to 25, or even 0 to 10percent by weight of at least one of ZrO₂ or HfO₂, based on the totalweight of the glass and glass-ceramic, respectively.

[0055] In another aspect, the present invention provides a method formaking ceramic, the method comprising:

[0056] combining (a) glass particles, the glass comprising at least 35(in some embodiments, preferably at least 40, 45, 50, 55, 60, 65, oreven at least 70) percent by weight Al₂O₃, based on the total weight ofthe glass, and a metal oxide other than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂,TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, and complex metal oxides thereof),wherein the glass contains not more than 10 (in some embodimentspreferably, less than 5 or even zero) percent by weight collectivelyAs₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weightof the glass, and (b) refractory particles (e.g., metal oxide particles,boride particles, carbide particles, nitride particles, diamondparticles, metallic particles, glass particles, and combinationsthereof) relative to the glass particles, the glass having a T_(g);

[0057] heating the glass particles above the T_(g) such that the glassparticles coalesce; and

[0058] cooling the glass to provide the ceramic. In some embodiments, ifthe metal oxide other than Al₂O₃ is CaO, then the glass particles andceramic further comprises at least one distinct crystalline phase of ametal oxide other than CaO. In some embodiments, if the metal oxideother than Al₂O₃ is ZrO₂, then the glass particles and ceramic furthercomprises at least one distinct crystalline phase of a metal oxide otherthan ZrO₂. In some embodiments, if the metal oxide other than Al₂O₃ isCaO or ZrO₂, then the glass particles and ceramic further comprises atleast one distinct crystalline phase of a metal oxide other than CaO orZrO₂. In some embodiments, the glass and ceramic comprise 0 to 50, 0 to25, or even 0 to 10 percent by weight of the metal oxide other thanAl₂O₃ (e.g., Y₂O₃, REO, ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, andcomplex metal oxides thereof), and/or 0 to 50, 0 to 25, or even 0 to 10percent by weight of at least one of ZrO₂ or HfO₂, based on the totalweight of the glass and ceramic, respectively.

[0059] In another aspect, the present invention provides a method formaking glass-ceramic, the method comprising:

[0060] combining (a) glass particles, the glass comprising at least 35(in some embodiments, preferably at least 40, 45, 50, 55, 60, 65, oreven at least 70) percent by weight Al₂O₃, based on the total weight ofthe glass, and metal oxide other than Al₂O₃ (e.g., Y₂O₃, REO, ZrO₂,TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, and complex metal oxides thereof),wherein the glass contains not more than 10 (in some embodimentspreferably, less than 5 or even zero) percent by weight collectivelyAs₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weightof the glass, and (b) refractory particles (e.g., metal oxide particles,boride particles, carbide particles, nitride particles, diamondparticles, metallic particles, glass particles, and combinationsthereof) relative to the glass particles, the glass having a T_(g);

[0061] heating the glass particles above the T_(g) such that the glassparticles coalesce;

[0062] cooling the glass to provide ceramic comprising glass; and

[0063] heat-treating the ceramic such that at least a portion of theglass is converted to a glass-ceramic. In some embodiments, if the metaloxide other than Al₂O₃ is CaO, then the glass further comprises a metaloxide other than Al₂O₃ or CaO at least a portion of which forms adistinct crystalline phase when the glass is crystallized, and theglass-ceramic further comprises at least one distinct crystalline phaseof a metal oxide other than CaO. In some embodiments, if the metal oxideother than Al₂O₃ is ZrO₂, then the glass further comprises a metal oxideother than Al₂O₃ or ZrO₂ at least a portion of which forms a distinctcrystalline phase when the glass is crystallized, and the glass-ceramicfurther comprises at least one distinct crystalline phase of a metaloxide other than ZrO₂. In some embodiments, if the metal oxide otherthan Al₂O₃ is CaO or ZrO₂, then the glass further comprises a metaloxide other than Al₂O₃, CaO, or ZrO₂ at least a portion of which forms adistinct crystalline phase when the glass is crystallized, and theglass-ceramic further comprises at least one distinct crystalline phaseof a metal oxide other than CaO or ZrO₂. In some embodiments, the glass,ceramic, and glass-ceramic comprise 0 to 50, 0 to 25, or even 0 to 10percent by weight of the metal oxide other than Al₂O₃ (e.g., Y₂O₃, REO,ZrO₂, TiO₂, CaO, Cr₂O₃, MgO, NiO, CuO, and complex metal oxidesthereof), and/or 0 to 50, 0 to 25, or even 0 to 10 percent by weight ofat least one of ZrO₂ or HfO₂, based on the total weight of the glass,ceramic, and glass-ceramic, respectively.

[0064] In this application:

[0065] “amorphous material” refers to material derived from a meltand/or a vapor phase that lacks any long range crystal structure asdetermined by X-ray diffraction and/or has an exothermic peakcorresponding to the crystallization of the amorphous material asdetermined by a DTA (differential thermal analysis) as determined by thetest described herein entitled “Differential Thermal Analysis”;

[0066] “ceramic” includes amorphous material, glass, crystallineceramic, glass-ceramic, and combinations thereof;

[0067] “complex metal oxide” refers to a metal oxide comprising two ormore different metal elements and oxygen (e.g., CeAl₁₁O₁₈, Dy₃Al₅O₁₂,MgAl₂O₄, and Y₃Al₅O₁₂);

[0068] “complex Al₂O₃.metal oxide” refers to a complex metal oxidecomprising, on a theoretical oxide basis, Al₂O₃ and one or more metalelements other than Al (e.g., CeAl₁₁O₁₈, Dy₃Al₅O₁₂, MgAl₂O₄, andY₃Al₅O₁₂);

[0069] “complex Al₂O₃.Y₂O₃” refers to a complex metal oxide comprising,on a theoretical oxide basis, Al₂O₃ and Y₂O₃ (e.g., Y₃Al₅O₁₂);

[0070] “complex Al₂O₃.REO” refers to a complex metal oxide comprising,on a theoretical oxide basis, Al₂O₃ and rare earth oxide (e.g.,CeAl₁₁O₁₈ and Dy₃Al₅O₁₂);

[0071] “glass” refers to amorphous material exhibiting a glasstransition temperature;

[0072] “glass-ceramic” refers to ceramics comprising crystals formed byheat-treating amorphous material;

[0073] “T_(g)” refers to the glass transition temperature as determinedin by the test described herein entitled “Differential ThermalAnalysis”;

[0074] “T_(g)” refers to the crystallization temperature as determinedin by the test described herein entitled “Differential ThermalAnalysis”;

[0075] “rare earth oxides” refers to cerium oxide (e.g., CeO₂),dysprosium oxide (e.g., Dy₂O₃), erbium oxide (e.g., Er₂O₃), europiumoxide (e.g., Eu₂O₃), gadolinium (e.g., Gd₂O₃), holmium oxide (e.g.,Ho₂O₃), lanthanum oxide (e.g., La₂O₃), lutetium oxide (e.g., Lu₂O₃),neodymium oxide (e.g., Nd₂O₃), praseodymium oxide (e.g., Pr₆O₁₁),samarium oxide (e.g., Sm₂O₃), terbium (e.g., Tb₂O₃), thorium oxide(e.g., Th₄O₇), thulium (e.g., Tm₂O₃), and ytterbium oxide (e.g., Yb₂O₃),and combinations thereof; and

[0076] “REO” refers to rare earth oxide(s).

[0077] Further, it is understood herein that unless it is stated that ametal oxide (e.g., Al₂O₃, complex Al₂O₃-metal oxide, etc.) iscrystalline, for example, in a glass-ceramic, it may be amorphous,crystalline, or portions amorphous and portions crystalline. For example1f a glass-ceramic comprises Al₂O₃ and ZrO₂, the Al₂O₃ and ZrO₂ may eachbe in an amorphous state, crystalline state, or portions in an amorphousstate and portions in a crystalline state, or even as a reaction productwith another metal oxide(s) (e.g., unless it is stated that, forexample, Al₂O₃ is present as crystalline Al₂O₃ or a specific crystallinephase of Al₂O₃ (e.g., alpha Al₂O₃), it may be present as crystallineAl₂O₃ and/or as part of one or more crystalline complex Al₂O₃.metaloxides.

[0078] Further, it is understood that glass-ceramics formed by heatingamorphous material not exhibiting a T_(g) may not actually compriseglass, but rather may comprise the crystals and amorphous material thatdoes not exhibiting a T_(g).

[0079] Amorphous materials and glass-ceramics according to the presentinvention can be made, formed as, or converted into particles (e.g.,glass beads (e.g., beads having diameters of at least 1 micrometers, 5micrometers, 10 micrometers, 25 micrometers, 50 micrometers, 100micrometers, 150 micrometers, 250 micrometers, 500 micrometers, 750micrometers, 1 mm, 5 mm, or even at least 10 mm)), articles (e.g.,plates), fibers, particles, and coatings (e.g., thin coatings).Amorphous materials and/or glass-ceramic particles and fibers areuseful, for example, as thermal insulation, filler, or reinforcingmaterial in composites (e.g., ceramic, metal, or polymeric matrixcomposites). The thin coatings can be useful, for example, as protectivecoatings in applications involving wear, as well as for thermalmanagement. Examples of articles according of the present inventioninclude kitchenware (e.g., plates), dental brackets, and reinforcingfibers, cutting tool inserts, abrasive materials, and structuralcomponents of gas engines, (e.g., valves and bearings). Other articlesinclude those having a protective coating of ceramic on the outersurface of a body or other substrate.

BRIEF DESCRIPTION OF THE DRAWING

[0080]FIG. 1 is a fragmentary cross-sectional schematic view of a coatedabrasive article including abrasive particles according to the presentinvention;

[0081]FIG. 2 is a perspective view of a bonded abrasive articleincluding abrasive particles according to the present invention; and

[0082]FIG. 3 is an enlarged schematic view of a nonwoven abrasivearticle including abrasive particles according to the present invention.

[0083]FIG. 4 is a DTA of the material prepared in Example 1;

[0084]FIG. 5 is a Scanning Electron Micrograph (SEM) of fracturedsurface of material prepared in Example 22;

[0085]FIG. 6 is a Scanning Electron Micrograph (SEM) of fracturedsurface of material prepared in Example 24;

[0086]FIG. 7 is a Scanning Electron Micrograph (SEM) of fracturedsurface of material prepared in Example 30;

[0087]FIG. 8 is a Scanning Electron Micrograph (SEM) of fracturedsurface of material prepared in Example 30;

[0088]FIG. 9 is a Scanning Electron Micrograph (SEM) of fracturedsurface of material prepared in Example 31;

[0089]FIG. 10 is a back scattered electron micrograph of the materialprepared in Example 32;

[0090]FIG. 11 is a DTA curve of Example 35 material;

[0091] FIGS. 12-15 are DTA curves of materials of Examples 36-39,respectively; and

[0092]FIG. 16 is an optical photomicrograph of a sectioned bar (2-mmthick) of the hot-pressed material of Example 47.

[0093]FIG. 17 is a scanning electron microscope (SEM) photomicrograph ofa polished section of heat-treated Example 47 material.

[0094]FIG. 18 is a DTA trace for Example 47 material.

[0095]FIG. 19 is an SEM photomicrograph of a polished section of Example65 material.

DETAILED DESCRIPTION

[0096] Some embodiments of amorphous materials (including glasses),glass-ceramics, abrasive particles according to the present inventioncomprising glass-ceramics, amorphous materials (including glasses) formaking the glass-ceramics, abrasive particles, etc. include thosecomprising Al₂O₃, and at least one other metal oxide (e.g., REO and; REOand at least one of ZrO₂ or HfO₂), wherein at least 80 (85, 90, 95, 97,98, 99, or even 100) percent by weight of the amorphous material,glass-ceramic, etc., as applicable, collectively comprises the comprisesthe Al₂O₃, and at least one other metal oxide, based on the total weightof the amorphous material, glass-ceramic, etc., as applicable.

[0097] Amorphous materials (e.g., glasses), ceramics comprising theamorphous material, particles comprising the amorphous material, etc.can be made, for example, by heating (including in a flame) theappropriate metal oxide sources to form a melt, desirably a homogenousmelt, and then rapidly cooling the melt to provide amorphous material.Embodiments of amorphous materials can be made, for example, by meltingthe metal oxide sources in any suitable furnace (e.g., an inductiveheated furnace, a gas-fired furnace, or an electrical furnace), or, forexample, in a plasma. The resulting melt is cooled (e.g., dischargingthe melt into a cooling media (e.g., high velocity air jets, liquids,metal plates (including chilled metal plates), metal rolls (includingchilled metal rolls), metal balls (including chilled metal balls), andthe like)).

[0098] Embodiments of amorphous material can be made utilizing flamefusion as disclosed, for example, in U.S. Pat. No. 6,254,981 (Castle),the disclosure of which is incorporated herein by reference. In thismethod, the metal oxide sources materials are fed (e.g., in the form ofparticles, sometimes referred to as “feed particles”) directly into aburner (e.g., a methane-air burner, an acetylene-oxygen burner, ahydrogen-oxygen burner, and like), and then quenched, for example, inwater, cooling oil, air, or the like. Feed particles can be formed, forexample, by grinding, agglomerating (e.g., spray-drying), melting, orsintering the metal oxide sources. The size of feed particles fed intothe flame generally determine the size of the resulting amorphousmaterial comprising particles.

[0099] Embodiments of amorphous materials can also be obtained by othertechniques, such as: laser spin melt with free fall cooling, Taylor wiretechnique, plasmatron technique, hammer and anvil technique, centrifugalquenching, air gun splat cooling, single roller and twin rollerquenching, roller-plate quenching and pendant drop melt extraction (see,e.g., Rapid Solidification of Ceramics, Brockway et. al, Metals AndCeramics Information Center, A Department of Defense InformationAnalysis Center, Columbus, Ohio, January, 1984, the disclosure of whichis incorporated here as a reference). Embodiments of amorphous materialsmay also be obtained by other techniques, such as: thermal (includingflame or laser or plasma-assisted) pyrolysis of suitable precursors,physical vapor synthesis (PVS) of metal precursors and mechanochemicalprocessing.

[0100] Useful amorphous material formulations include those at or near aeutectic composition(s) (e.g., binary and ternary eutecticcompositions). In addition to compositions disclosed herein, othercompositions, including quaternary and other higher order eutecticcompositions, may be apparent to those skilled in the art afterreviewing the present disclosure.

[0101] Typically, amorphous materials, and the glass-ceramics accordingto the present invention made there from, have x, y, and z dimensionseach perpendicular to each other, and wherein each of the x, y, and zdimensions is at least 25 micrometers. In some embodiments, the x, y,and z dimensions is at least 30 micrometers, 35 micrometers, 40micrometers, 45 micrometers, 50 micrometers, 75 micrometers, 100micrometers, 150 micrometers, 200 micrometers, 250 micrometers, 500micrometers, 1000 micrometers, 2000 micrometers, 2500 micrometers, 1 mm,5 mm, or even at least 10 mm. Sources, including commercial sources, of(on a theoretical oxide basis) Al₂O₃ include bauxite (including bothnatural occurring bauxite and synthetically produced bauxite), calcinedbauxite, hydrated aluminas (e.g., boehmite, and gibbsite), aluminum,Bayer process alumina, aluminum ore, gamma alumina, alpha alumina,aluminum salts, aluminum nitrates, and combinations thereof. The Al₂O₃source may contain, or only provide, Al₂O₃. Alternatively, the Al₂O₃source may contain, or provide Al₂O₃, as well as one or more metaloxides other than Al₂O₃ (including materials of or containing complexAl₂O₃.metal oxides (e.g., Dy₃Al₅O₁₂, Y₃Al₅O₁₂, CeAl₁₁O₁₈, etc.)).

[0102] Sources, including commercial sources, of rare earth oxidesinclude rare earth oxide powders, rare earth metals, rareearth-containing ores (e.g., bastnasite and monazite), rare earth salts,rare earth nitrates, and rare earth carbonates. The rare earth oxide(s)source may contain, or only provide, rare earth oxide(s). Alternatively,the rare earth oxide(s) source may contain, or provide rare earthoxide(s), as well as one or more metal oxides other than rare earthoxide(s) (including materials of or containing complex rare earthoxide•other metal oxides (e.g., Dy₃Al₅O₁₂, CeAl₁₁O₁₈, etc.)).

[0103] Sources, including commercial sources, of (on a theoretical oxidebasis) Y₂O₃ include yttrium oxide powders, yttrium, yttrium-containingores, and yttrium salts (e.g., yttrium carbonates, nitrates, chlorides,hydroxides, and combinations thereof). The Y₂O₃ source may contain, oronly provide, Y₂O₃. Alternatively, the Y₂O₃ source may contain, orprovide Y₂O₃, as well as one or more metal oxides other than Y₂O₃(including materials of or containing complex Y₂O₃.metal oxides (e.g.,Y₃Al₅O₁₂)).

[0104] Sources, including commercial sources, of (on a theoretical oxidebasis) ZrO₂ include zirconium oxide powders, zircon sand, zirconium,zirconium-containing ores, and zirconium salts (e.g., zirconiumcarbonates, acetates, nitrates, chlorides, hydroxides, and combinationsthereof). In addition, or alternatively, the ZrO₂ source may contain, orprovide ZrO₂, as well as other metal oxides such as hafnia. Sources,including commercial sources, of (on a theoretical oxide basis) HfO₂include hafnium oxide powders, hafnium, hafnium-containing ores, andhafnium salts. In addition, or alternatively, the HfO₂ source maycontain, or provide HfO₂, as well as other metal oxides such as ZrO₂.

[0105] Other useful metal oxide may also include, on a theoretical oxidebasis, BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, Li₂O, MgO, MnO, NiO, Na₂O,Sc₂O₃, SrO, TiO₂, ZnO, and combinations thereof. Sources, includingcommercial sources, include the oxides themselves, complex oxides, ores,carbonates, acetates, nitrates, chlorides, hydroxides, etc. These metaloxides are added to modify a physical property of the resulting abrasiveparticles and/or improve processing. These metal oxides are typicallyare added anywhere from 0 to 50% by weight, in some embodimentspreferably 0 to 25% by weight and more preferably 0 to 50% by weight ofthe glass-ceramic depending, for example, upon the desired property.

[0106] In some embodiments, it may be advantageous for at least aportion of a metal oxide source (in some embodiments, preferably, 10 15,20, 25, 30, 35, 40, 45, or even at least 50 percent by weight) to beobtained by adding particulate, metallic material comprising at leastone of a metal (e.g., Al, Ca, Cu, Cr, Fe, Li, Mg, Ni, Ag, Ti, Zr, andcombinations thereof), M, that has a negative enthalpy of oxideformation or an alloy thereof to the melt, or otherwise metal them withthe other raw materials. Although not wanting to be bound by theory, itis believed that the heat resulting from the exothermic reactionassociated with the oxidation of the metal is beneficial in theformation of a homogeneous melt and resulting amorphous material. Forexample, it is believed that the additional heat generated by theoxidation reaction within the raw material eliminates or minimizesinsufficient heat transfer, and hence facilitates formation andhomogeneity of the melt, particularly when forming amorphous particleswith x, y, and z dimensions over 150 micrometers. It is also believedthat the availability of the additional heat aids in driving variouschemical reactions and physical processes (e.g., densification, andspherodization) to completion. Further, it is believed for someembodiments, the presence of the additional heat generated by theoxidation reaction actually enables the formation of a melt, whichotherwise is difficult or otherwise not practical due to high meltingpoint of the materials. Further, the presence of the additional heatgenerated by the oxidation reaction actually enables the formation ofamorphous material that otherwise could not be made, or could not bemade in the desired size range. Another advantage of the inventioninclude, in forming the amorphous materials, that many of the chemicaland physical processes such as melting, densification and spherodizingcan be achieved in a short time, so that very high quench rates be canachieved. For additional details, see copending application having U.S.Ser. No. ______ (Attorney Docket No. 56931US007), filed the same date asthe instant application, the disclosure of which is incorporated hereinby reference.

[0107] The particular selection of metal oxide sources and otheradditives for making ceramics according to the present inventiontypically takes into account, for example, the desired composition andmicrostructure of the resulting ceramics, the desired degree ofcrystallinity, if any, the desired physical properties (e.g., hardnessor toughness) of the resulting ceramics, avoiding or minimizing thepresence of undesirable impurities, the desired characteristics of theresulting ceramics, and/or the particular process (including equipmentand any purification of the raw materials before and/or during fusionand/or solidification) being used to prepare the ceramics.

[0108] In some instances, it may be preferred to incorporate limitedamounts of metal oxides selected from the group consisting of: Na₂O,P₂O₅, SiO₂, TeO₂, V₂O₃, and combinations thereof. Sources, includingcommercial sources, include the oxides themselves, complex oxides, ores,carbonates, acetates, nitrates, chlorides, hydroxides, etc. These metaloxides may be added, for example, to modify a physical property of theresulting abrasive particles and/or improve processing. These metaloxides when used are typically are added from greater than 0 to 20% byweight, preferably greater than 0 to 5% by weight and more preferablygreater than 0 to 2% by weight of the glass-ceramic depending, forexample, upon the desired property.

[0109] The addition of certain metal oxides may alter the propertiesand/or crystalline structure or microstructure of a glass-ceramicaccording to the present invention, as well as the processing of the rawmaterials and intermediates in making the glass-ceramic. For example,oxide additions such as MgO, CaO, Li₂O, and Na₂O have been observed toalter both the T_(g) (for a glass) and T_(x) (wherein T_(x) is thecrystallization temperature) of amorphous material. Although not wishingto be bound by theory, it is believed that such additions influenceglass formation. Further, for example, such oxide additions may decreasethe melting temperature of the overall system (i.e., drive the systemtoward lower melting eutectic), and ease of amorphousmaterial-formation. Complex eutectics in multi component systems(quaternary, etc.) may result in better amorphous material-formingability. The viscosity of the liquid melt and viscosity of the glass inits' “working” range may also be affected by the addition of certainmetal oxides such as MgO, CaO, Li₂O, and Na₂O. It is also within thescope of the present invention to incorporate at least one of halogens(e.g., fluorine and chlorine), or chalcogenides (e.g., sulfides,selenides, and tellurides) into the amorphous materials, and theglass-ceramics made there from.

[0110] Crystallization of the amorphous material and ceramic comprisingthe amorphous material may also be affected by the additions of certainmaterials. For example, certain metals, metal oxides (e.g., titanatesand zirconates), and fluorides, for example, may act as nucleationagents resulting in beneficial heterogeneous nucleation of crystals.Also, addition of some oxides may change nature of metastable phasesdevitrifying from the amorphous material upon reheating. In anotheraspect, for ceramics comprising crystalline ZrO₂, it may be desirable toadd metal oxides (e.g., Y₂O₃, TiO₂, CaO, and MgO) that are known tostabilize tetragonal/cubic form of ZrO₂.

[0111] The metal oxide sources and other additives can be in any formsuitable to the process and equipment being used to make theglass-ceramics according to the present invention. The raw materials canbe melted and quenched using techniques and equipment known in the artfor making oxide amorphous materials and amorphous metals. Desirablecooling rates include those of 50K/s and greater. Cooling techniquesknown in the art include roll-chilling. Roll-chilling can be carriedout, for example, by melting the metal oxide sources at a temperaturetypically 20-200° C. higher than the melting point, andcooling/quenching the melt by spraying it under high pressure (e.g.,using a gas such as air, argon, nitrogen or the like) onto a high-speedrotary roll(s). Typically, the rolls are made of metal and are watercooled. Metal book molds may also be useful for cooling/quenching themelt.

[0112] Other techniques for forming melts, cooling/quenching melts,and/or otherwise forming amorphous material include vapor phasequenching, melt-extraction, plasma spraying, and gas or centrifugalatomization. Vapor phase quenching can be carried out, for example, bysputtering, wherein the metal alloys or metal oxide sources are formedinto a sputtering target(s) which are used. The target is fixed at apredetermined position in a sputtering apparatus, and a substrate(s) tobe coated is placed at a position opposing the target(s). Typicalpressures of 10-3 torr of oxygen gas and Ar gas, discharge is generatedbetween the target(s) and a substrate(s), and Ar or oxygen ions collideagainst the target to start reaction sputtering, thereby depositing afilm of composition on the substrate. For additional details regardingplasma spraying, see, for example, copending application having U.S.Ser. No. ______ (Attorney Docket No. 57980US002), filed the same date asthe instant application, the disclosure of which is incorporated hereinby reference.

[0113] Gas atomization involves melting feed particles to convert themto melt. A thin stream of such melt is atomized through contact with adisruptive air jet (i.e., the stream is divided into fine droplets). Theresulting substantially discrete, generally ellipsoidal amorphousmaterial comprising particles (e.g., beads) are then recovered. Examplesof bead sizes include those having a diameter in a range of about 5micrometers to about 3 mm. Melt-extraction can be carried out, forexample, as disclosed in U.S. Pat. No. 5,605,870 (Strom-Olsen et al.),the disclosure of which is incorporated herein by reference.Containerless glass forming techniques utilizing laser beam heating asdisclosed, for example, in PCT application having Publication No. WO01/27046 A1, published Apr. 4, 2001, the disclosure of which isincorporated herein by reference, may also be useful in making materialsaccording to the present invention.

[0114] The cooling rate is believed to affect the properties of thequenched amorphous material. For instance, glass transition temperature,density and other properties of glass typically change with coolingrates.

[0115] Typically, it is preferred that the bulk material comprises atleast 50, 60, 75, 80, 85, 90, 95, 98, 99, or even 100 percent by weightof the amorphous material.

[0116] Rapid cooling may also be conducted under controlled atmospheres,such as a reducing, neutral, or oxidizing environment to maintain and/orinfluence the desired oxidation states, etc. during cooling. Theatmosphere can also influence amorphous material formation byinfluencing crystallization kinetics from undercooled liquid. Forexample, larger undercooling of Al₂O₃ melts without crystallization hasbeen reported in argon atmosphere as compared to that in air.

[0117] The microstructure or phase composition(glassy/amorphous/crystalline) of a material can be determined in anumber of ways. Various information can be obtained using opticalmicroscopy, electron microscopy, differential thermal analysis (DTA),and x-ray diffraction (XRD), for example.

[0118] Using optical microscopy, amorphous material is typicallypredominantly transparent due to the lack of light scattering centerssuch as crystal boundaries, while crystalline material shows acrystalline structure and is opaque due to light scattering effects.

[0119] A percent amorphous yield can be calculated for beads using a−100+120 mesh size fraction (i.e., the fraction collected between150-micrometer opening size and 125-micrometer opening size screens).The measurements are done in the following manner. A single layer ofbeads is spread out upon a glass slide. The beads are observed using anoptical microscope. Using the crosshairs in the optical microscopeeyepiece as a guide, beads that lay along a straight line are countedeither amorphous or crystalline depending on their optical clarity. Atotal of 500 beads are counted and a percent amorphous yield isdetermined by the amount of amorphous beads divided by total beadscounted.

[0120] Using DTA, the material is classified as amorphous if thecorresponding DTA trace of the material contains an exothermiccrystallization event (T_(x)). If the same trace also contains anendothermic event (T_(g)) at a temperature lower than T_(x) it isconsidered to consist of a glass phase. If the DTA trace of the materialcontains no such events, it is considered to contain crystalline phases.

[0121] Differential thermal analysis (DTA) can be conducted using thefollowing method. DTA runs can be made (using an instrument such as thatobtained from Netzsch Instruments, Selb, Germany under the tradedesignation “NETZSCH STA 409 DTA/TGA”) using a −140+170 mesh sizefraction (i.e., the fraction collected between 105-micrometer openingsize and 90-micrometer opening size screens). An amount of each screenedsample (typically about 400 milligrams (mg)) is placed in a100-microliter Al₂O₃ sample holder. Each sample is heated in static airat a rate of 10° C./minute from room temperature (about 25° C.) to 1100°C.

[0122] Using powder x-ray diffraction, XRD, (using an x-raydiffractometer such as that obtained under the trade designation“PHILLIPS XRG 3100” from Phillips, Mahwah, N.J., with copper K oilradiation of 1.54050 Angstrom) the phases present in a material can bedetermined by comparing the peaks present in the XRD trace of thecrystallized material to XRD patterns of crystalline phases provided inJCPDS (Joint Committee on Powder Diffraction Standards) databases,published by International Center for Diffraction Data. Furthermore, anXRD can be used qualitatively to determine types of phases. The presenceof a broad diffused intensity peak is taken as an indication of theamorphous nature of a material. The existence of both a broad peak andwell-defined peaks is taken as an indication of existence of crystallinematter within an amorphous matrix.

[0123] The initially formed amorphous material or ceramic (includingglass prior to crystallization) may be larger in size than that desired.The amorphous material or ceramic can be converted into smaller piecesusing crushing and/or comminuting techniques known in the art, includingroll crushing, canary milling, jaw crushing, hammer milling, ballmilling, jet milling, impact crushing, and the like. In some instances,it is desired to have two or multiple crushing steps. For example, afterthe ceramic is formed (solidified), it may be in the form of larger thandesired. The first crushing step may involve crushing these relativelylarge masses or “chunks” to form smaller pieces. This crushing of thesechunks may be accomplished with a hammer mill, impact crusher or jawcrusher. These smaller pieces may then be subsequently crushed toproduce the desired particle size distribution. In order to produce thedesired particle size distribution (sometimes referred to as grit sizeor grade), it may be necessary to perform multiple crushing steps. Ingeneral the crushing conditions are optimized to achieve the desiredparticle shape(s) and particle size distribution. Resulting particlesthat are of the desired size may be recrushed if they are too large, or“recycled” and used as a raw material for re-melting if they are toosmall.

[0124] The shape of the ceramic (including glass prior tocrystallization) may depend, for example, on the composition and/ormicrostructure of the ceramic, the geometry in which it was cooled, andthe manner in which the ceramic is crushed (i.e., the crushing techniqueused). In general, where a “blocky” shape is preferred, more energy maybe employed to achieve this shape. Conversely, where a “sharp” shape ispreferred, less energy may be employed to achieve this shape. Thecrushing technique may also be changed to achieve different desiredshapes. For some particles an average aspect ratio ranging from 1:1 to5:1 is typically desired, and in some embodiments 1.25:1 to 3:1, or even1.5:1 to 2.5:1.

[0125] It is also within the scope of the present invention, forexample, to directly form ceramic (including glass prior tocrystallization) may in desired shapes. For example, ceramic (includingglass prior to crystallization) may be formed (including molded) bypouring or forming the melt into a mold.

[0126] It is also within the scope of the present invention, forexample, to fabricate the ceramic (including glass prior tocrystallization) by coalescing. This coalescing step in essence forms alarger sized body from two or more smaller particles. For example,amorphous material comprising particles (obtained, for example, bycrushing) (including beads and microspheres), fibers, etc. may formedinto a larger particle size. For example, ceramic (including glass priorto crystallization), may also be provided by heating, for example,particles comprising the amorphous material, and/or fibers, etc. abovethe T_(g) such that the particles, etc. coalesce to form a shape andcooling the coalesced shape. The temperature and pressure used forcoalescing may depend, for example, upon composition of the amorphousmaterial and the desired density of the resulting material. Thetemperature should below glass crystallization temperature, and forglasses, greater than the glass transition temperature. In certainembodiments, the heating is conducted at at least one temperature in arange of about 850° C. to about 1100° C. (in some embodiments,preferably 900° C. to 1000° C.). Typically, the amorphous material isunder pressure (e.g., greater than zero to 1 GPa or more) duringcoalescence to aid the coalescence of the amorphous material. In oneembodiment, a charge of the particles, etc. is placed into a die andhot-pressing is performed at temperatures above glass transition whereviscous flow of glass leads to coalescence into a relatively large part.Examples of typical coalescing techniques include hot pressing, hotisostatic pressure, hot extrusion and the like. Typically, it isgenerally preferred to cool the resulting coalesced body before furtherheat treatment. After heat treatment if so desired, the coalesced bodymay be crushed to smaller particle sizes or a desired particle sizedistribution.

[0127] It is also within the scope of the present invention to conductadditional heat-treatment to further improve desirable properties of thematerial. For example, hot-isostatic pressing may be conducted (e.g., attemperatures from about 900° C. to about 1400° C.) to remove residualporosity, increasing the density of the material. Optionally, theresulting, coalesced article can be heat-treated to provideglass-ceramic, crystalline ceramic, or ceramic otherwise comprisingcrystalline ceramic.

[0128] Coalescence of the amorphous material and/or glass-ceramic (e.g.,particles) may also be accomplished by a variety of methods, includingpressureless or pressure sintering (e.g., sintering, plasma assistedsintering, hot pressing, HIPing, hot forging, hot extrusion, etc.).

[0129] Heat-treatment can be carried out in any of a variety of ways,including those known in the art for heat-treating glass to provideglass-ceramics. For example, heat-treatment can be conducted in batches,for example, using resistive, inductively or gas heated furnaces.Alternatively, for example, heat-treatment can be conductedcontinuously, for example, using rotary kilns. In the case of a rotarykiln, the material is fed directly into a kiln operating at the elevatedtemperature. The time at the elevated temperature may range from a fewseconds (in some embodiments even less than 5 seconds) to a few minutesto several hours. The temperature may range anywhere from 900° C. to1600° C., typically between 1200° C. to 1500° C. It is also within thescope of the present invention to perform some of the heat-treatment inbatches (e.g., for the nucleation step) and another continuously (e.g.,for the crystal growth step and to achieve the desired density). For thenucleation step, the temperature typically ranges between about 900° C.to about 1100° C., in some embodiments, preferably in a range from about925° C. to about 1050° C. Likewise for the density step, the temperaturetypically is in a range from about 1100° C. to about 1600° C., in someembodiments, preferably in a range from about 1200° C. to about 1500° C.This heat treatment may occur, for example, by feeding the materialdirectly into a furnace at the elevated temperature. Alternatively, forexample, the material may be feed into a furnace at a much lowertemperature (e.g., room temperature) and then heated to desiredtemperature at a predetermined heating rate. It is within the scope ofthe present invention to conduct heat-treatment in an atmosphere otherthan air. In some cases it might be even desirable to heat-treat in areducing atmosphere(s). Also, for, example, it may be desirable toheat-treat under gas pressure as in, for example, hot-isostatic press,or in gas pressure furnace. It is within the scope of the presentinvention to convert (e.g., crush) the resulting article or heat-treatedarticle to provide particles (e.g., abrasive particles).

[0130] The amorphous material is heat-treated to at least partiallycrystallize the amorphous material to provide glass-ceramic. Theheat-treatment of certain glasses to form glass-ceramics is well knownin the art. The heating conditions to nucleate and grow glass-ceramicsare known for a variety of glasses. Alternatively, one skilled in theart can determine the appropriate conditions from aTime-Temperature-Transformation (TTT) study of the glass usingtechniques known in the art. One skilled in the art, after reading thedisclosure of the present invention should be able to provide TTT curvesfor glasses according to the present invention, determine theappropriate nucleation and/or crystal growth conditions to provideglass-ceramics according to the present invention.

[0131] Typically, glass-ceramics are stronger than the amorphousmaterials from which they are formed. Hence, the strength of thematerial may be adjusted, for example, by the degree to which theamorphous material is converted to crystalline ceramic phase(s).Alternatively, or in addition, the strength of the material may also beaffected, for example, by the number of nucleation sites created, whichmay in turn be used to affect the number, and in turn the size of thecrystals of the crystalline phase(s). For additional details regardingforming glass-ceramics, see, for example Glass-Ceramics, P. W. McMillan,Academic Press, Inc., 2nd edition, 1979, the disclosure of which isincorporated herein by reference.

[0132] For example, during heat-treatment of some exemplary amorphousmaterials for making glass-ceramics according to present invention,formation of phases such as La₂Zr₂O₇, and, if ZrO₂ is present,cubic/tetragonal ZrO₂, in some cases monoclinic ZrO₂, have been observedat temperatures above about 900° C. Although not wanting to be bound bytheory, it is believed that zirconia-related phases are the first phasesto nucleate from the amorphous material. Formation of Al₂O₃, ReAlO₃(wherein Re is at least one rare earth cation), ReAl₁₁O₁₈, Re₃Al₅O₁₂,Y₃Al₅O₁₂, etc. phases are believed to generally occur at temperaturesabove about 925° C. Typically, crystallite size during this nucleationstep is on order of nanometers. For example, crystals as small as 10-15nanometers have been observed. For at least some embodiments,heat-treatment at about 1300° C. for about 1 hour provides a fullcrystallization. In generally, heat-treatment times for each of thenucleation and crystal growth steps may range of a few seconds (in someembodiments even less than 5 seconds) to several minutes to an hour ormore.

[0133] The size of the resulting crystals can typically controlled atleast in part by the nucleation and/or crystallization times and/ortemperatures. Although it is generally preferred to have small crystals(e.g., on the order not greater than a micrometer, or even not greaterthan a nanometer) glass-ceramics according to the present invention maybe made with larger crystal sizes (e.g., at least 1-10 micrometers, atleast 10-25 micrometers, at least 50-100 micrometers, or even graterthan 100 micrometers). Although not wanting to be bound by theory, it isgenerally believed in the art that the finer the size of the crystals(for the same density), the higher the mechanical properties (e.g.,hardness and strength) of the ceramic.

[0134] Examples of crystalline phases which may be present inembodiments of abrasive particles according to the present inventioninclude: Al₂O₃ (e.g., α-Al₂O₃), Y₂O₃, REO, HfO₂ ZrO₂ (e.g., cubic ZrO₂and tetragonal ZrO₂), BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, Li₂O, MgO, MnO,NiO, Na₂O, P₂O₅, Sc₂O₃, SiO₂, SrO, TeO₂, TiO₂, V₂O₃, Y₂O₃, ZnO, “complexmetal oxides” (including “complex Al₂O₃.metal oxide (e.g., complexAl₂O₃.REO (e.g., ReAlO₃ (e.g., GdAl_(O) ₃ LaAlO₃), ReAl₁₁O₁₈ (e.g.,LaAl₁₁O₁₈,), and Re₃Al₅O₁₂ (e.g., Dy₃Al₅O₁₂)), complex Al₂O₃.Y₂O₃ (e.g.,Y₃Al₅O₁₂), and complex ZrO₂.REO (e.g., Re₂Zr₂O₇ (e.g., La₂Zr₂O₇))), andcombinations thereof

[0135] It is also with in the scope of the present invention tosubstitute a portion of the yttrium and/or aluminum cations in a complexAl₂O₃.metal oxide (e.g., complex Al₂O₃.Y₂O₃ (e.g., yttrium aluminateexhibiting a garnet crystal structure)) with other cations. For example,a portion of the Al cations in a complex Al₂O₃.Y₂O₃ may be substitutedwith at least one cation of an element selected from the groupconsisting of: Cr, Ti, Sc, Fe, Mg, Ca, Si, Co, and combinations thereof.For example, a portion of the Y cations in a complex Al₂O₃.Y₂O₃ may besubstituted with at least one cation of an element selected from thegroup consisting of: Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Th, Tm,Yb, Fe, Ti, Mn, V, Cr, Co, Ni, Cu, Mg, Ca, Sr, and combinations thereof.Similarly, it is also with in the scope of the present invention tosubstitute a portion of the aluminum cations in alumina. For example,Cr, Ti, Sc, Fe, Mg, Ca, Si, and Co can substitute for aluminum in thealumina. The substitution of cations as described above may affect theproperties (e.g. hardness, toughness, strength, thermal conductivity,etc.) of the fused material.

[0136] It is also with in the scope of the present invention tosubstitute a portion of the rare earth and/or aluminum cations in acomplex Al₂O₃.metal oxide (e.g., complex Al₂O₃.REO) with other cations.For example, a portion of the Al cations in a complex Al₂O₃.REO may besubstituted with at least one cation of an element selected from thegroup consisting of: Cr, Ti, Sc, Fe, Mg, Ca, Si, Co, and combinationsthereof. For example, a portion of the Y cations in a complex Al₂O₃.REOmay be substituted with at least one cation of an element selected fromthe group consisting of: Y, Fe, Ti, Mn, V, Cr, Co, Ni, Cu, Mg, Ca, Sr,and combinations thereof. Similarly, it is also with in the scope of thepresent invention to substitute a portion of the aluminum cations inalumina. For example, Cr, Ti, Sc, Fe, Mg, Ca, Si, and Co can substitutefor aluminum in the alumina. The substitution of cations as describedabove may affect the properties (e.g. hardness, toughness, strength,thermal conductivity, etc.) of the fused material.

[0137] The average crystal size can be determined by the line interceptmethod according to the ASTM standard E 112-96 “Standard Test Methodsfor Determining Average Grain Size”. The sample is mounted in mountingresin (such as that obtained under the trade designation “TRANSOPTICPOWDER” from Buehler, Lake Bluff, Ill.) typically in a cylinder of resinabout 2.5 cm in diameter and about 1.9 cm high. The mounted section isprepared using conventional polishing techniques using a polisher (suchas that obtained from Buehler, Lake Bluff, Ill. under the tradedesignation “ECOMET 3”). The sample is polished for about 3 minutes witha diamond wheel, followed by 5 minutes of polishing with each of 45, 30,15, 9, 3, and 1-micrometer slurries. The mounted and polished sample issputtered with a thin layer of gold-palladium and viewed using ascanning electron microscopy (such as the JEOL SEM Model JSM 840A). Atypical back-scattered electron (BSE) micrograph of the microstructurefound in the sample is used to determine the average crystal size asfollows. The number of crystals that intersect per unit length (NL) of arandom straight line drawn across the micrograph are counted. Theaverage crystal size is determined from this number using the followingequation.${{Average}\quad {Crystal}\quad {Size}} = \frac{1.5}{N_{L}M}$

[0138] Where N_(L) is the number of crystals intersected per unit lengthand M is the magnification of the micrograph.

[0139] Some embodiments of the present invention include glass-ceramicscomprising alpha alumina having at least one of an average crystal sizenot greater than 150 nanometers.

[0140] Some embodiments of the present invention include glass-ceramicscomprising alpha alumina, wherein at least 90 (in some embodimentspreferably, 95, or even 100) percent by number of the alpha aluminapresent in such portion have crystal sizes not greater than 200nanometers.

[0141] Some embodiments of the present invention include glass-ceramicscomprising alpha Al₂O₃, crystalline ZrO₂, and a first complexAl₂O₃.Y₂O₃, and wherein at least one of the alpha Al₂O₃, the crystallineZrO₂, or the first complex Al₂O₃-Y₂O₃ has an average crystal size notgreater than 150 nanometers. In some embodiments preferably, theglass-ceramics further comprise a second, different complex Al₂O₃.Y₂O₃.In some embodiments preferably, the glass-ceramics further comprise acomplex Al₂O₃-REO.

[0142] Some embodiments of the present invention include glass-ceramicscomprising a first complex Al₂O₃.Y₂O₃, a second, different complexAl₂O₃.Y₂O₃, and crystalline ZrO₂, and wherein for at least one of thefirst complex Al₂O₃.Y₂O₃, the second complex Al₂O₃.Y₂O₃, or thecrystalline ZrO₂, at least 90 (in some embodiments preferably, 95, oreven 100) percent by number of the crystal sizes thereof are not greaterthan 200 nanometers. In some embodiments preferably, the glass-ceramicsfurther comprise a second, different complex Al₂O₃.Y₂O₃. In someembodiments preferably, the glass-ceramics further comprise a complexAl₂O₃.REO.

[0143] Some embodiments of the present invention include glass-ceramicscomprising alpha Al₂O₃, crystalline ZrO₂, and a first complex Al₂O₃.REO,and wherein at least one of the alpha Al₂O₃, the crystalline ZrO₂, orthe first complex Al₂O₃.REO has an average crystal size not greater than150 nanometers. In some embodiments preferably, the glass-ceramicsfurther comprise a second, different complex Al₂O₃.REO. In someembodiments preferably, the glass-ceramics further comprise a complexAl₂O₃.Y₂O₃.

[0144] Some embodiments of the present invention include glass-ceramicscomprising a first complex Al₂O₃.REO, a second, different complexAl₂O₃.REO, and crystalline ZrO₂, and wherein for at least one of thefirst complex Al₂O₃.REO, the second complex Al₂O₃.REO, or thecrystalline ZrO₂, at least 90 (in some embodiments preferably, 95, oreven 100) percent by number of the crystal sizes thereof are not greaterthan 200 nanometers. In some embodiments preferably, the glass-ceramicsfurther comprise a complex Al₂O₃.Y₂O₃.

[0145] Some embodiments of the present invention include glass-ceramicscomprising a first complex Al₂O₃.Y₂O₃, a second, different complexAl₂O₃.Y₂O₃, and crystalline ZrO₂, and wherein at least one of the firstcomplex Al₂O₃.Y₂O₃, the second, different complex Al₂O₃.Y₂O₃, or thecrystalline ZrO₂ has an average crystal size not greater than 150nanometers. In some embodiments preferably, the glass-ceramics furthercomprise a second, different complex Al₂O₃.Y₂O₃. In some embodimentspreferably, the glass-ceramics further comprise a complex Al₂O₃.REO.

[0146] Some embodiments of the present invention include glass-ceramicscomprising a first complex Al₂O₃.Y₂O₃, a second, different complexAl₂O₃.Y₂O₃, and crystalline ZrO₂, and wherein for at least one of thefirst complex Al₂O₃.Y₂O₃, the second, different complex Al₂O₃-Y₂O₃, orthe crystalline ZrO₂, at least 90 (in some embodiments preferably, 95,or even 100) percent by number of the crystal sizes thereof are notgreater than 200 nanometers. In some embodiments preferably, theglass-ceramics further comprise a complex Al₂O₃.REO.

[0147] Some embodiments of the present invention include glass-ceramicscomprising a first complex Al₂O₃.REO, a second, different complexAl₂O₃.REO, and crystalline ZrO₂, and wherein at least one of the firstcomplex Al₂O₃.REO, the second, different complex Al₂O₃.REO, or thecrystalline ZrO₂ has an average crystal size not greater than 150nanometers. In some embodiments preferably, the glass-ceramics furthercomprise a second, different complex Al₂O₃.REO. In some embodimentspreferably, the glass-ceramics further comprise a complex Al₂O₃ Y₂O₃.

[0148] Some embodiments of the present invention include glass-ceramicscomprising a first complex Al₂O₃.REO, a second, different complexAl₂O₃-REO, and crystalline ZrO₂, and wherein for at least one of thefirst complex Al₂O₃.REO, the second, different complex Al₂O₃.REO, or thecrystalline ZrO₂, at least 90 (in some embodiments preferably, 95, oreven 100) percent by number of the crystal sizes thereof are not greaterthan 200 nanometers. In some embodiments preferably, the glass-ceramicsfurther comprise a complex Al₂O₃.Y₂O₃.

[0149] In some embodiments, glass-ceramics according to the presentinvention comprise at least 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume crystallites, wherein the crystallites have an averagesize of less than 1 micrometer. In some embodiments, glass-ceramicsaccording to the present invention comprise not greater than at least75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystallites, wherein the crystallites have an average size not greaterthan 0.5 micrometer. In some embodiments, glass-ceramics according tothe present invention comprise less than at 75, 80, 85, 90, 95, 97, 98,99, or even 100 percent by volume crystallites, wherein the crystalliteshave an average size not greater than 0.3 micrometer. In someembodiments, glass-ceramics according to the present invention compriseless than at least 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percentby volume crystallites, wherein the crystallites have an average sizenot greater than 0.15 micrometer.

[0150] Crystals formed by heat-treating amorphous to provide embodimentsof glass-ceramics according to the present invention may be, forexample, equiaxed, columnar, or flattened splat-like features.

[0151] Although an amorphous material, glass-ceramic, etc. according tothe present invention may be in the form of a bulk material, it is alsowithin the scope of the present invention to provide compositescomprising an amorphous material, glass-ceramic, etc. according to thepresent invention. Such a composite may comprise, for example, a phaseor fibers (continuous or discontinuous) or particles (includingwhiskers) (e.g., metal oxide particles, boride particles, carbideparticles, nitride particles, diamond particles, metallic particles,glass particles, and combinations thereof) dispersed in an amorphousmaterial, glass-ceramic, etc. according to the present invention,invention or a layered-composite structure (e.g., a gradient ofglass-ceramic to amorphous material used to make the glass-ceramicand/or layers of different compositions of glass-ceramics).

[0152] Typically, the (true) density, sometimes referred to as specificgravity, of ceramics according to the present invention is typically atleast 70% of theoretical density. More desirably, the (true) density ofceramic according to the present invention is at least 75%, 80%, 85%,90%, 92%, 95%, 96%, 97%, 98%, 99%, 99.5% or even 100% of theoreticaldensity. Abrasive particles according to the present invention havedensities of at least 85%, 90%, 92%, 95%, 96%, 97%, 98%, 99%, 99.5% oreven 100% of theoretical density.

[0153] The average hardness of the material of the present invention canbe determined as follows. Sections of the material are mounted inmounting resin (obtained under the trade designation “TRANSOPTIC POWDER”from Buehler, Lake Bluff, Ill.) typically in a cylinder of resin about2.5 cm in diameter and about 1.9 cm high. The mounted section isprepared using conventional polishing techniques using a polisher (suchas that obtained from Buehler, Lake Bluff, Ill. under the tradedesignation “ECOMET 3”). The sample is polished for about 3 minutes witha diamond wheel, followed by 5 minutes of polishing with each of 45, 30,15, 9, 3, and 1-micrometer slurries. The microhardness measurements aremade using a conventional microhardness tester (such as that obtainedunder the trade designation “MITUTOYO MVK-VL” from Mitutoyo Corporation,Tokyo, Japan) fitted with a Vickers indenter using a 100-gram indentload. The microhardness measurements are made according to theguidelines stated in ASTM Test Method E384 Test Methods forMicrohardness of Materials (1991), the disclosure of which isincorporated herein by reference.

[0154] In some embodiments, glass-ceramic according to the presentinvention have an average hardness of at least 13 GPa (in someembodiments preferably, at least 14, 15, 16, 17, or even at least 18GPa). Abrasive particles according to the present invention have anaverage hardness of at least 15 GPa, in some embodiments, at least 16GPa, at least 17 GPa, or even at least 18 GPa.

[0155] Additional details regarding amorphous materials andglass-ceramics, including making, using, and properties thereof, can befound in application having U.S. Ser. Nos. 09/922,526, 09/922,527, and09/922,530, filed Aug. 2, 2001, and U.S. Ser. Nos. ______ (AttorneyDocket Nos. 56931US005, 56931US006, 56931US007, 56931US009, 56931US010,57980US002, and 57981US002, filed the same date as the instantapplication, the disclosures of which are incorporated herein byreference.

[0156] Abrasive particles according to the present invention generallycomprise crystalline ceramic (in some embodiments, preferably at least75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5, or even 100percent by volume) crystalline ceramic.

[0157] Abrasive particles according to the present invention can bescreened and graded using techniques well known in the art, includingthe use of industry recognized grading standards such as ANSI (AmericanNational Standard Institute), FEPA (Federation Europeenne des Fabricantsde Products Abrasifs), and JIS (Japanese Industrial Standard). Abrasiveparticles according to the present invention may be used in a wide rangeof particle sizes, typically ranging in size from about 0.1 to about5000 micrometers, more typically from about 1 to about 2000 micrometers;desirably from about 5 to about 1500 micrometers, more desirably fromabout 100 to about 1500 micrometers.

[0158] ANSI grade designations include: ANSI 4, ANSI 6, ANSI 8, ANSI 16,ANSI 24, ANSI 36, ANSI 40, ANSI 50, ANSI 60, ANSI 80, ANSI 100, ANSI120, ANSI 150, ANSI 180, ANSI 220, ANSI 240, ANSI 280, ANSI 320, ANSI360, ANSI 400, and ANSI 600. Preferred ANSI grades comprising abrasiveparticles according to the present invention are ANSI 8-220. FEPA gradedesignations include P8, P12, P16, P24, P36, P40, P50, P60, P80, P100,P120, P150, P180, P220, P320, P400, P500, P600, P800, P1000, and P1200.Preferred FEPA grades comprising abrasive particles according to thepresent invention are P12-P220. JIS grade designations include JIS8,JIS12, JIS16, JIS24, JIS36, JIS46, JIS54, JIS60, JIS80, JIS10, JIS150,JIS180, JIS220, JIS240, JIS280, JIS320, JIS360, JIS400, JIS400, JIS600,JIS800, JIS 1000, JIS 1500, JIS2500, JIS4000, JIS6000, JIS8000, andJIS10,000. Preferred JIS grades comprising abrasive particles accordingto the present invention are JIS8-220.

[0159] After crushing and screening, there will typically be a multitudeof different abrasive particle size distributions or grades. Thesemultitudes of grades may not match a manufacturer's or supplier's needsat that particular time. To minimize inventory, it is possible torecycle the off demand grades back into melt to form amorphous material.This recycling may occur after the crushing step, where the particlesare in large chunks or smaller pieces (sometimes referred to as “fines”)that have not been screened to a particular distribution.

[0160] In another aspect, the present invention provides a method formaking abrasive particles, the method comprising heat-treating amorphous(e.g., glass) comprising particles such that at least a portion of theamorphous material converts to a glass-ceramic to provide abrasiveparticles comprising the glass-ceramic. The present invention alsoprovides a method for making abrasive particles comprising aglass-ceramic, the method comprising heat-treating amorphous materialsuch that at least a portion of the amorphous material converts to aglass-ceramic, and crushing the resulting heat-treated material toprovide the abrasive particles. When crushed, glass tends to providesharper particles than crushing significantly crystallizedglass-ceramics or crystalline material.

[0161] In another aspect, the present invention provides agglomerateabrasive grains each comprise a plurality of abrasive particlesaccording to the present invention bonded together via a binder. Inanother aspect, the present invention provides an abrasive article(e.g., coated abrasive articles, bonded abrasive articles (includingvitrified, resinoid, and metal bonded grinding wheels, cutoff wheels,mounted points, and honing stones), nonwoven abrasive articles, andabrasive brushes) comprising a binder and a plurality of abrasiveparticles, wherein at least a portion of the abrasive particles areabrasive particles (including where the abrasive particles areagglomerated) according to the present invention. Methods of making suchabrasive articles and using abrasive articles are well known to thoseskilled in the art. Furthermore, abrasive particles according to thepresent invention can be used in abrasive applications that utilizeabrasive particles, such as slurries of abrading compounds (e.g.,polishing compounds), milling media, shot blast media, vibratory millmedia, and the like.

[0162] Coated abrasive articles generally include a backing, abrasiveparticles, and at least one binder to hold the abrasive particles ontothe backing. The backing can be any suitable material, including cloth,polymeric film, fibre, nonwoven webs, paper, combinations thereof, andtreated versions thereof. The binder can be any suitable binder,including an inorganic or organic binder (including thermally curableresins and radiation curable resins). The abrasive particles can bepresent in one layer or in two layers of the coated abrasive article.

[0163] An example of a coated abrasive article according to the presentinvention is depicted in FIG. 1. Referring to this figure, coatedabrasive article according to the present invention 1 has a backing(substrate) 2 and abrasive layer 3. Abrasive layer 3 includes abrasiveparticles according to the present invention 4 secured to a majorsurface of backing 2 by make coat 5 and size coat 6. In some instances,a supersize coat (not shown) is used.

[0164] Bonded abrasive articles typically include a shaped mass ofabrasive particles held together by an organic, metallic, or vitrifiedbinder. Such shaped mass can be, for example, in the form of a wheel,such as a grinding wheel or cutoff wheel. The diameter of grindingwheels typically is about 1 cm to over 1 meter; the diameter of cut offwheels about 1 cm to over 80 cm (more typically 3 cm to about 50 cm).The cut off wheel thickness is typically about 0.5 mm to about 5 cm,more typically about 0.5 mm to about 2 cm. The shaped mass can also bein the form, for example, of a honing stone, segment, mounted point,disc (e.g. double disc grinder) or other conventional bonded abrasiveshape. Bonded abrasive articles typically comprise about 3-50% by volumebond material, about 30-90% by volume abrasive particles (or abrasiveparticle blends), up to 50% by volume additives (including grindingaids), and up to 70% by volume pores, based on the total volume of thebonded abrasive article.

[0165] A preferred form is a grinding wheel. Referring to FIG. 2,grinding wheel according to the present invention 10 is depicted, whichincludes abrasive particles according to the present invention 11,molded in a wheel and mounted on hub 12.

[0166] Nonwoven abrasive articles typically include an open porous loftypolymer filament structure having abrasive particles according to thepresent invention distributed throughout the structure and adherentlybonded therein by an organic binder. Examples of filaments includepolyester fibers, polyamide fibers, and polyaramid fibers. In FIG. 3, aschematic depiction, enlarged about 100×, of a typical nonwoven abrasivearticle according to the present invention is provided. Such a nonwovenabrasive article according to the present invention comprises fibrousmat 50 as a substrate, onto which abrasive particles according to thepresent invention 52 are adhered by binder 54.

[0167] Useful abrasive brushes include those having a plurality ofbristles unitary with a backing (see, e.g., U.S. Pat. Nos. 5,427,595(Pihl et al.), 5,443,906 (Pihl et al.), U.S. Pat. No. 5,679,067 (Johnsonet al.), and U.S. Pat. No. 5,903,951 (Ionta et al.), the disclosure ofwhich is incorporated herein by reference). Desirably, such brushes aremade by injection molding a mixture of polymer and abrasive particles.

[0168] Suitable organic binders for making abrasive articles includethermosetting organic polymers. Examples of suitable thermosettingorganic polymers include phenolic resins, urea-formaldehyde resins,melamine-formaldehyde resins, urethane resins, acrylate resins,polyester resins, aminoplast resins having pendant α,β-unsaturatedcarbonyl groups, epoxy resins, acrylated urethane, acrylated epoxies,and combinations thereof. The binder and/or abrasive article may alsoinclude additives such as fibers, lubricants, wetting agents,thixotropic materials, surfactants, pigments, dyes, antistatic agents(e.g., carbon black, vanadium oxide, graphite, etc.), coupling agents(e.g., silanes, titanates, zircoaluminates, etc.), plasticizers,suspending agents, and the like. The amounts of these optional additivesare selected to provide the desired properties. The coupling agents canimprove adhesion to the abrasive particles and/or filler. The binderchemistry may thermally cured, radiation cured or combinations thereof.Additional details on binder chemistry may be found in U.S. Pat. Nos.4,588,419 (Caul et al.), U.S. Pat. No. 4,751,138 (Tumey et al.), andU.S. Pat. No. 5,436,063 (Follett et al.), the disclosures of which areincorporated herein by reference.

[0169] More specifically with regard to vitrified bonded abrasives,vitreous bonding materials, which exhibit an amorphous structure and aretypically hard, are well known in the art. In some cases, the vitreousbonding material includes crystalline phases. Bonded, vitrified abrasivearticles according to the present invention may be in the shape of awheel (including cut off wheels), honing stone, mounted pointed or otherconventional bonded abrasive shape. A preferred vitrified bondedabrasive article according to the present invention is a grinding wheel.

[0170] Examples of metal oxides that are used to form vitreous bondingmaterials include: silica, silicates, alumina, soda, calcia, potassia,titania, iron oxide, zinc oxide, lithium oxide, magnesia, boria,aluminum silicate, borosilicate glass, lithium aluminum silicate,combinations thereof, and the like. Typically, vitreous bondingmaterials can be formed from composition comprising from 10 to 100%glass frit, although more typically the composition comprises 20% to 80%glass frit, or 30% to 70% glass frit. The remaining portion of thevitreous bonding material can be a non-frit material. Alternatively, thevitreous bond may be derived from a non-frit containing composition.Vitreous bonding materials are typically matured at a temperature(s) ina range of about 700° C. to about 1500° C., usually in a range of about800° C. to about 1300° C., sometimes in a range of about 900° C. toabout 1200° C., or even in a range of about 950° C. to about 1100° C.The actual temperature at which the bond is matured depends, forexample, on the particular bond chemistry.

[0171] Preferred vitrified bonding materials may include thosecomprising silica, alumina (desirably, at least 10 percent by weightalumina), and boria (desirably, at least 10 percent by weight boria). Inmost cases the vitrified bonding material further comprise alkali metaloxide(s) (e.g., Na₂O and K₂O) (in some cases at least 10 percent byweight alkali metal oxide(s)).

[0172] Binder materials may also contain filler materials or grindingaids, typically in the form of a particulate material. Typically, theparticulate materials are inorganic materials. Examples of usefulfillers for this invention include: metal carbonates (e.g., calciumcarbonate (e.g., chalk, calcite, marl, travertine, marble andlimestone), calcium magnesium carbonate, sodium carbonate, magnesiumcarbonate), silica (e.g., quartz, glass beads, glass bubbles and glassfibers) silicates (e.g., talc, clays, (montmorillonite) feldspar, mica,calcium silicate, calcium metasilicate, sodium aluminosilicate, sodiumsilicate) metal sulfates (e.g., calcium sulfate, barium sulfate, sodiumsulfate, aluminum sodium sulfate, aluminum sulfate), gypsum,vermiculite, wood flour, aluminum trihydrate, carbon black, metal oxides(e.g., calcium oxide (lime), aluminum oxide, titanium dioxide), andmetal sulfites (e.g., calcium sulfite).

[0173] In general, the addition of a grinding aid increases the usefullife of the abrasive article. A grinding aid is a material that has asignificant effect on the chemical and physical processes of abrading,which results in improved performance. Although not wanting to be boundby theory, it is believed that a grinding aid(s) will (a) decrease thefriction between the abrasive particles and the workpiece being abraded,(b) prevent the abrasive particles from “capping” (i.e., prevent metalparticles from becoming welded to the tops of the abrasive particles),or at least reduce the tendency of abrasive particles to cap, (c)decrease the interface temperature between the abrasive particles andthe workpiece, or (d) decreases the grinding forces.

[0174] Grinding aids encompass a wide variety of different materials andcan be inorganic or organic based. Examples of chemical groups ofgrinding aids include waxes, organic halide compounds, halide salts andmetals and their alloys. The organic halide compounds will typicallybreak down during abrading and release a halogen acid or a gaseoushalide compound. Examples of such materials include chlorinated waxeslike tetrachloronaphtalene, pentachloronaphthalene, and polyvinylchloride. Examples of halide salts include sodium chloride, potassiumcryolite, sodium cryolite, ammonium cryolite, potassiumtetrafluoroboate, sodium tetrafluoroborate, silicon fluorides, potassiumchloride, and magnesium chloride. Examples of metals include, tin, lead,bismuth, cobalt, antimony, cadmium, and iron titanium. Othermiscellaneous grinding aids include sulfur, organic sulfur compounds,graphite, and metallic sulfides. It is also within the scope of thepresent invention to use a combination of different grinding aids, andin some instances this may produce a synergistic effect. The preferredgrinding aid is cryolite; the most preferred grinding aid is potassiumtetrafluoroborate.

[0175] Grinding aids can be particularly useful in coated abrasive andbonded abrasive articles. In coated abrasive articles, grinding aid istypically used in the supersize coat, which is applied over the surfaceof the abrasive particles. Sometimes, however, the grinding aid is addedto the size coat. Typically, the amount of grinding aid incorporatedinto coated abrasive articles are about 50-300 g/m² (desirably, about80-160 g/m²). In vitrified bonded abrasive articles grinding aid istypically impregnated into the pores of the article.

[0176] The abrasive articles can contain 100% abrasive particlesaccording to the present invention, or blends of such abrasive particleswith other abrasive particles and/or diluent particles. However, atleast about 2% by weight, desirably at least about 5% by weight, andmore desirably about 30-100% by weight, of the abrasive particles in theabrasive articles should be abrasive particles according to the presentinvention. In some instances, the abrasive particles according thepresent invention may be blended with another abrasive particles and/ordiluent particles at a ratio between 5 to 75% by weight, about 25 to 75%by weight about 40 to 60% by weight, or about 50% to 50% by weight(i.e., in equal amounts by weight). Examples of suitable conventionalabrasive particles include fused aluminum oxide (including white fusedalumina, heat-treated aluminum oxide and brown aluminum oxide), siliconcarbide, boron carbide, titanium carbide, diamond, cubic boron nitride,garnet, fused alumina-zirconia, and sol-gel-derived abrasive particles,and the like. The sol-gel-derived abrasive particles may be seeded ornon-seeded. Likewise, the sol-gel-derived abrasive particles may berandomly shaped or have a shape associated with them, such as a rod or atriangle. Examples of sol gel abrasive particles include those describedU.S. Pat. Nos. 4,314,827 (Leitheiser et al.), 4,518,397 (Leitheiser etal.), U.S. Pat. No. 4,623,364 (Cottringer et al.), U.S. Pat. No.4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.), U.S. Pat.No. 4,881,951 (Wood et al.), U.S. Pat. No. 5,011,508 (Wald et al.), U.S.Pat. No. 5,090,968 (Pellow), U.S. Pat. No. 5,139,978 (Wood), U.S. Pat.No. 5,201,916 (Berg et al.), U.S. Pat. No. 5,227,104 (Bauer), U.S. Pat.No. 5,366,523 (Rowenhorst et al.), U.S. Pat. Nos. 5,429,647 (Larmie),5,498,269 (Larmie), and 5,551,963 (Larmie), the disclosures of which areincorporated herein by reference. Additional details concerning sinteredalumina abrasive particles made by using alumina powders as a rawmaterial source can also be found, for example, in U.S. Pat. No.5,259,147 (Falz), U.S. Pat. No. 5,593,467 (Monroe), and U.S. Pat. No.5,665,127 (Moltgen), the disclosures of which are incorporated herein byreference. Additional details concerning fused abrasive particles, canbe found, for example, in U.S. Pat. No. 1,161,620 (Coulter), U.S. Pat.No. 1,192,709 (Tone), U.S. Pat. No. 1,247,337 (Saunders et al.), U.S.Pat. No. 1,268,533 (Allen), and U.S. Pat. No. 2,424,645 (Baumann et al.)U.S. Pat. No. 3,891,408 (Rowse et al.), U.S. Pat. No. 3,781,172 (Pett etal.), U.S. Pat. No. 3,893,826 (Quinan et al.), U.S. Pat. No. 4,126,429(Watson), U.S. Pat. No. 4,457,767 (Poon et al.), U.S. Pat. No. 5,023,212(Dubots et. al), U.S. Pat. No. 5,143,522 (Gibson et al.), and U.S. Pat.No. 5,336,280 (Dubots et. al), and applications having U.S. Serial Nos.09,495,978, 09/496,422, 09/496,638, and 09/496,713, each filed on Feb.2, 2000, and, Ser. Nos. 09/618,876, 09/618,879, 09/619,106, 09/619,191,09/619,192, 09/619,215, 09/619,289, 09/619,563, 09/619,729, 09/619,744,and 09/620,262, each filed on Jul. 19, 2000, and Ser. No. 09/772,730,filed Jan. 30, 2001, the disclosures of which are incorporated herein byreference. In some instances, blends of abrasive particles may result inan abrasive article that exhibits improved grinding performance incomparison with abrasive articles comprising 100% of either type ofabrasive particle.

[0177] If there is a blend of abrasive particles, the abrasive particletypes forming the blend may be of the same size. Alternatively, theabrasive particle types may be of different particle sizes. For example,the larger sized abrasive particles may be abrasive particles accordingto the present invention, with the smaller sized particles being anotherabrasive particle type. Conversely, for example, the smaller sizedabrasive particles may be abrasive particles according to the presentinvention, with the larger sized particles being another abrasiveparticle type.

[0178] Examples of suitable diluent particles include marble, gypsum,flint, silica, iron oxide, aluminum silicate, glass (including glassbubbles and glass beads), alumina bubbles, alumina beads and diluentagglomerates. Abrasive particles according to the present invention canalso be combined in or with abrasive agglomerates. Abrasive agglomerateparticles typically comprise a plurality of abrasive particles, abinder, and optional additives. The binder may be organic and/orinorganic. Abrasive agglomerates may be randomly shape or have apredetermined shape associated with them. The shape may be a block,cylinder, pyramid, coin, square, or the like. Abrasive agglomerateparticles typically have particle sizes ranging from about 100 to about5000 micrometers, typically about 250 to about 2500 micrometers.Additional details regarding abrasive agglomerate particles may befound, for example, in U.S. Pat. No. 4,311,489 (Kressner), U.S. Pat. No.4,652,275 (Bloecher et al.), U.S. Pat. No. 4,799,939 (Bloecher et al.),U.S. Pat. No. 5,549,962 (Holmes et al.), and U.S. Pat. No. 5,975,988(Christianson), and applications having U.S. Ser. Nos. 09/688,444 and09/688,484, filed Oct. 16, 2000, the disclosures of which areincorporated herein by reference.

[0179] The abrasive particles may be uniformly distributed in theabrasive article or concentrated in selected areas or portions of theabrasive article. For example, in a coated abrasive, there may be twolayers of abrasive particles. The first layer comprises abrasiveparticles other than abrasive particles according to the presentinvention, and the second (outermost) layer comprises abrasive particlesaccording to the present invention. Likewise in a bonded abrasive, theremay be two distinct sections of the grinding wheel. The outermostsection may comprise abrasive particles according to the presentinvention, whereas the innermost section does not. Alternatively,abrasive particles according to the present invention may be uniformlydistributed throughout the bonded abrasive article.

[0180] Further details regarding coated abrasive articles can be found,for example, in U.S. Pat. No. 4,734,104 (Broberg), U.S. Pat. No.4,737,163 (Larkey), U.S. Pat. No. 5,203,884 (Buchanan et al.), U.S. Pat.No. 5,152,917 (Pieper et al.), U.S. Pat. No. 5,378,251 (Culler et al.),U.S. Pat. No. 5,417,726 (Stout et al.), U.S. Pat. No. 5,436,063 (Follettet al.), U.S. Pat. No. 5,496,386 (Broberg et al.), U.S. Pat. No. 5,609,706 (Benedict et al.), U.S. Pat. No. 5,520,711 (Helmin), U.S. Pat.No. 5,954,844 (Law et al.), U.S. Pat. No. 5,961,674 (Gagliardi et al.),and U.S. Pat. No. 5,975,988 (Christinason), the disclosures of which areincorporated herein by reference. Further details regarding bondedabrasive articles can be found, for example, in U.S. Pat. No. 4,543,107(Rue), U.S. Pat. No. 4,741,743 (Narayanan et al.), U.S. Pat. No.4,800,685 (Haynes et al.), U.S. Pat. No. 4,898,597 (Hay et al.), U.S.Pat. No. 4,997,461 (Markhoff-Matheny et al.), U.S. Pat. No. 5,037,453(Narayanan et al.), U.S. Pat. No. 5,110,332 (Narayanan et al.), and U.S.Pat. No. 5,863,308 (Qi et al.) the disclosures of which are incorporatedherein by reference. Further details regarding vitreous bonded abrasivescan be found, for example, in U.S. Pat. No. 4,543,107 (Rue), U.S. Pat.No. 4,898,597 (Hay et al.), U.S. Pat. No. 4,997,461 (Markhoff-Matheny etal.), U.S. Pat. No. 5,094,672 (Giles Jr. et al.), U.S. Pat. Nos.5,118,326 (Sheldon et al.), 5,131,926(Sheldon et al.), 5,203,886(Sheldon et al.), U.S. Pat. No. 5,282,875 (Wood et al.), U.S. Pat. No.5,738,696 (Wu et al.), and U.S. Pat. No. 5,863,308 (Qi), the disclosuresof which are incorporated herein by reference. Further details regardingnonwoven abrasive articles can be found, for example, in U.S. Pat. No.2,958,593 (Hoover et al.), the disclosure of which is incorporatedherein by reference.

[0181] The present invention provides a method of abrading a surface,the method comprising contacting at least one abrasive particleaccording to the present invention, with a surface of a workpiece; andmoving at least of one the abrasive particle or the contacted surface toabrade at least a portion of said surface with the abrasive particle.Methods for abrading with abrasive particles according to the presentinvention range of snagging (i.e., high pressure high stock removal) topolishing (e.g., polishing medical implants with coated abrasive belts),wherein the latter is typically done with finer grades (e.g., less ANSI220 and finer) of abrasive particles. The abrasive particle may also beused in precision abrading applications, such as grinding cam shaftswith vitrified bonded wheels. The size of the abrasive particles usedfor a particular abrading application will be apparent to those skilledin the art.

[0182] Abrading with abrasive particles according to the presentinvention may be done dry or wet. For wet abrading, the liquid may beintroduced supplied in the form of a light mist to complete flood.Examples of commonly used liquids include: water, water-soluble oil,organic lubricant, and emulsions. The liquid may serve to reduce theheat associated with abrading and/or act as a lubricant. The liquid maycontain minor amounts of additives such as bactericide, antifoamingagents, and the like.

[0183] Abrasive particles according to the present invention may be usedto abrade workpieces such as aluminum metal, carbon steels, mild steels,tool steels, stainless steel, hardened steel, titanium, glass, ceramics,wood, wood like materials, paint, painted surfaces, organic coatedsurfaces and the like. The applied force during abrading typicallyranges from about 1 to about 100 kilograms.

[0184] Other examples of uses of embodiments of amorphous materialsand/or glass-ceramics according to the present invention include assolid electrolytes in such applications as solid state batteries, solidoxide fuel cells and other electrochemical devices; as hosts forradioactive wastes and surplus actinides; as oxidation catalysts; asoxygen monitoring sensors; as hosts for fluorescence centers; durable IRtransmitting window materials; and armor. For example, pyrochlore typeof rare earth zirconium oxides (Re₂Zr₂O₇) are known to be useful phasesfor the above-mentioned radioactive wastes, surplus actinides, oxidationcatalysts, oxygen monitoring sensors, and fluorescence centersapplications. Further, for example, Ce-containing mixed oxides are knownas oxidation catalysts. Although not wanting to be bound by theory, itis believed that the redox properties and the relatively high oxygenstorage capacity of the Ce-containing mixed oxides aid in oxidationcatalysts. With regard to durable IR transmitting window materialsapplications uses include those involving moisture, impact by solid andliquid particles, high temperatures, and rapid heating rates.

[0185] Advantages and embodiments of this invention are furtherillustrated by the following examples, but the particular materials andamounts thereof recited in these examples, as well as other conditionsand details, should not be construed to unduly limit this invention. Allparts and percentages are by weight unless otherwise indicated. Unlessotherwise stated, all examples contained no significant amount of SiO₂,B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃, and V₂O₅.

EXAMPLES Examples 1-20

[0186] A 250-ml polyethylene bottle (7.3-cm diameter) was charged with a50-gram mixture of various powders (as shown below in Table 1, withsources of the raw materials listed in Table 2), 75 grams of isopropylalcohol, and 200 grams of alumina milling media (cylindrical shape, bothheight and diameter of 0.635 cm; 99.9% alumina; obtained from Coors,Golden, Colo.). The contents of the polyethylene bottle were milled for16 hours at 60 revolutions per minute (rpm). After the milling, themilling media were removed and the slurry was poured onto a warm(approximately 75° C.) glass (“PYREX”) pan and dried. The dried mixturewas screened through a 70-mesh screen (212-micrometer opening size) withthe aid of a paint brush.

[0187] After grinding and screening, the mixture of milled feedparticles was fed slowly (0.5 gram/minute) into a hydrogen/oxygen torchflame to melt the particles. The torch used to melt the particles,thereby generating molten droplets, was a Bethlehem bench burner PM2DModel B obtained from Bethlehem Apparatus Co., Hellertown, Pa. Hydrogenand oxygen flow rates for the torch were as follows. For the inner ring,the hydrogen flow rate was 8 standard liters per minute (SLPM) and theoxygen flow rate was 3.5 SLPM. For the outer ring, the hydrogen flowrate was 23 SLPM and the oxygen flow rate was 12 SLPM. The dried andsized particles were fed slowly (0.5 gram/minute) into the torch flamewhich melted the particles and carried them into a 19-liter (5-gallon)cylindrical container (30 cm diameter by 34 cm height) of continuouslycirculating, turbulent water to rapidly quench the molten droplets. Theangle at which the flame hit the water was approximately 45°, and theflame length, burner to water surface, was approximately 18 centimeters(cm). The resulting molten and rapidly quenched particles were collectedand dried at 110° C. The particles were spherical in shape and varied insize from a few micrometers (i.e., microns) up to 250 micrometers.

[0188] A percent amorphous yield was calculated from the resultingflame-formed beads using a −100+120 mesh size fraction (i.e., thefraction collected between 150-micrometer opening size and125-micrometeropening size screens). The measurements were done in thefollowing manner. A single layer of beads was spread out upon a glassslide. The beads were observed using an optical microscope. Using thecrosshairs in the optical microscope eyepiece as a guide, beads that layalong a straight line were counted either amorphous or crystallinedepending on their optical clarity. A total of 500 beads were countedand a percent amorphous yield was determined by the amount of amorphousbeads divided by total beads counted.

[0189] Materials prepared in Examples 12 through 20 were amorphous asdetermined by visual inspection, but the quantitative analysis accordingto the above procedure was not performed. Amorphous material istypically transparent due to the lack of light scattering centers suchas crystal boundaries, while the crystalline particles show acrystalline structure and are opaque due to light scattering effects.

[0190] The phase composition (glassy/amorphous/crystalline) wasdetermined through Differential Thermal Analysis (DTA) as describedbelow. The material was classified as amorphous if the corresponding DTAtrace of the material contained an exothermic crystallization event(T_(x)). If the same trace also contained an endothermic event (T_(g))at a temperature lower than T_(x) it was considered to consist of aglass phase. If the DTA trace of the material contained no such events,it was considered to contain crystalline phases.

[0191] Differential thermal analysis (DTA) was conducted using thefollowing method. DTA runs were made (using an instrument obtained fromNetzsch Instruments, Selb, Germany under the trade designation “NETZSCHSTA 409 DTA/TGA”) using a −140+170 mesh size fraction (i.e., thefraction collected between 105-micrometer opening size and 90-micrometeropening size screens). The amount of each screened sample placed in a100-microliter Al₂O₃ sample holder was about 400 milligrams. Each samplewas heated in static air at a rate of 10° C./minute from roomtemperature (about 25° C.) to 1100° C.

[0192] Referring to FIG. 4, line 123 is the plotted DTA data for theExample 1 material. Referring to FIG. 4, line 123, the materialexhibited an endothermic event at temperature around 872° C., asevidenced by the downward curve of line 123. It is believed this eventwas due to the glass transition (T_(g)) of the glass material. At about958° C., an exothermic event was observed as evidenced by the sharp peakin line 123. It is believed that this event was due to thecrystallization (T_(g)) of the material. These T_(g) and T_(x) valuesfor other examples, except for Examples 15-20, are reported in Table 1below. TABLE 1 Percent final Percent Glass transition/ Batch Weightpercent Final weight alumina from amorphous crystallization Exampleamounts, g of components percent alumina % Al metal yield temperaturesEx. 1 Al₂O₃: 19.3 Al₂O₃: 38.5 ALZ La₂O₃: 21.3 La₂O₃: 42.5 882° C. ZrO₂:9.5 ZrO₂: 19.0 38.5 0 98 932° C. Ex. 2 Al₂O₃: 16.7 Al₂O₃: 33.3 AYZ Al:8.8 Al: 17.6 Y₂O₃: 16 Y₂O₃: 31.9 900° C. ZrO₂: 8.6 ZrO₂: 17.2 57.5 50 89935° C. Ex. 3 Al₂O₃: 20.5 Al₂O₃: 41.0 872° C. AGdZ Gd₂O₃: 20.5 Gd₂O₃:41.0 ZrO₂: 9 ZrO₂: 18 41.0 0 94 Ex. 4 Al₂O₃: 19.5 Al₂O₃: 39.1 AY Al:10.3 Al: 20.7 894° C. Y₂O₃: 20.1 Y₂O₃: 40.3 66 50 93 943° C. Ex. 5Al₂O₃: 18.8 Al₂O₃: 37.7 AYMg Al: 10.0 Al: 19.9 MgO: 0.0 MgO: 0.0 Mg: 1.8Mg: 3.6 848° C. Y₂O₃: 19.4 Y₂O₃: 38.8 62.7 50 93 996° C. Ex. 6 Al₂O₃:18.1 Al₂O₃: 36.2 AYMg Al: 9.6 Al: 19.2 MgO: 0.0 MgO: 0.0 Mg: 3.7 Mg: 7.3832° C. Y₂O₃: 18.6 Y₂O₃: 37.3 59.4 50 81 884° C. Ex. 7 Al₂O₃: 17.0Al₂O₃: 33.9 none AZ Al: 9.0 Al: 18.0 58.5 50 63 959° C. ZrO₂: 24.1 ZrO₂:48.1 Ex. 8 Al₂O₃: 15.5 Al₂O₃: 31.0 AZ-Ti Al: 8.2 Al: 16.4 ZrO₂: 22.0ZrO₂: 44.0 none TiO₂: 4.3 TiO₂: 8.6 54 50 79 936° C. Ex. 9 Al₂O₃: 12.3Al₂O₃: 24.5 AZ-La Al: 6.5 Al: 13.0 ZrO₂: 17.4 ZrO₂: 34.8 889° C. La₂O₃:13.8 La₂O₃: 27.7 44 50 94 918° C. Ex. 10 Al₂O₃: 9.1 Al₂O₃: 18.2 AZ-LaAl: 4.8 Al: 9.6 ZrO₂: 13.0 ZrO₂: 25.9 868° C. La₂O₃: 23.1 La₂O₃: 46.2 3450 96 907° C. Ex. 11 Al₂O₃: 7.5 Al₂O₃: 15.0 AZ-La Al: 4.0 Al: 8.0 ZrO₂:17.0 ZrO₂: 34.0 870° C. La₂O₃: 21.4 La₂O₃: 42.8 28 50 93 898° C. Ex. 12Al₂O₃: 20.3 Al₂O₃: 40.6 ACZ ZrO₂: 9.0 ZrO₂: 18.0 838° C. La₂O₃: 20.7La₂O₃: 41.4 40.6 0 NA 908° C. Ex. 13 Al₂O₃: 15.6 Al₂O₃: 31.2 ALZ/ La₂O₃:17 La₂O₃: 34 CaF₂ ZrO₂: 7.4 ZrO₂: 14.8 CaF₂: 10 CaF2: 20 none 37.04 0 NA676° C. Ex. 14 Al₂O₃: 17.87 Al₂O₃: 35.73 ALZ/ La₂O₃: 21.08 La₂O₃: 42.17P₂O₅ ZrO₂: 8.55 ZrO₂: 17.1 P₂O₅: 2.5 P₂O₅: 5 857° C. 35.73 0 NA 932° C.Ex. 15 Al₂O₃: 17.87 Al₂O₃: 35.73 ALZ/ La₂O₃: 21.08 La₂O₃: 42.17 Nb₂O₅ZrO₂: 8.55 ZrO₂: 17.1 Nb₂O₅: 2.5 Nb₂O₅: 5 35.73 0 NA NA Ex. 16 Al₂O₃:17.87 Al₂O₃: 35.73 ALZ/ La₂O₃: 21.08 La₂O₃: 42.17 Ta₂O₅ ZrO₂: 8.55 ZrO₂:17.1 Ta₂O₅: 2.5 Ta₂O₅: 5 NA 35.73 0 NA Ex. 17 Al₂O₃: 17.87 Al₂O₃: 35.73ALZ/ La₂O₃: 21.08 La₂O₃: 42.17 SrO ZrO₂: 8.55 ZrO₂: 17.1 SrO: 2.5 SrO: 5NA 35.73 0 NA Ex. 18 Al₂O₃: 17.87 Al₂O₃: 35.73 ALZ/ La₂O₃: 21.08 La₂O₃:42.17 Mn₂O₃ ZrO₂: 8.55 ZrO₂: 17.1 Mn₂O₃: 2.5 Mn₂O₃: 5 NA 35.73 0 NA Ex.19 Al₂O₃: 18.25 Al₂O₃: 36.5 ALZ/ La₂O₃: 21.52 La₂O₃: 43.04 Fe₂O₃ ZrO₂:8.73 ZrO₂: 17.46 Fe₂O₃: 1.5 Fe₂O₃: 3 NA 36.5 0 NA Ex. 20 Al₂O₃: 18.25Al₂O₃: 36.5 ALZ/ La₂O₃: 21.52 La₂O₃: 43.04 Cr₂O₃ ZrO₂: 8.73 ZrO₂: 17.46Cr₂O₃: 1.5 Cr₂O₃: 3 NA 36.5 0 NA

[0193] TABLE 2 Raw Material Source Alumina particles (Al₂O₃) Obtainedfrom Alcoa Industrial Chemicals, Bauxite, AR, under the tradedesignation “A16SG” Aluminum particles (Al) Obtained from Alfa Aesar,Ward Hill, MA Cerium oxide particles Obtained from Rhone-Poulence,France Gadolinium oxide particles Obtained from Molycorp Inc., MountainPass, CA Lanthanum oxide particles (La₂O₃) Obtained from Molycorp Inc.,Mountain Pass, CA and calcined at 700° C. for 6 hours prior to batchmixing. Magnesium particles (Mg) Obtained from Alfa Aesar, Ward Hill, MAMagnesium oxide particles (MgO) Obtained from BDH Chemicals Ltd, Poole,England Titanium oxide particles (TiO₂) Obtained from Kemira, Savannah,GA, under the trade designation “Unitane 0-110” Yttrium oxide particles(Y₂O₃) Obtained from H.C. Stark Newton, MA Zirconium oxide particles(ZrO₂) Obtained from Zirconia Sales, Inc. of Marietta, GA under thetrade designation “DK-2” Calcium fluoride particles (CaF₂) Obtained fromAldrich, Milwaukee, WI Phosphorous oxide particles (P₂O₅) Obtained fromAldrich, Milwaukee, WI Niobium oxide particles (Nb₂O₅) Obtained fromAldrich, Milwaukee, WI Tantalum oxide particles (Ta₂O₅) Obtained fromAldrich, Milwaukee, WI Strontium oxide particles (SrO) Obtained fromAldrich, Milwaukee, WI Manganese oxide particles (Mn₂O₃) Obtained fromAldrich, Milwaukee, WI Iron oxide particles (Fe₂O₃) Obtained fromAldrich, Milwaukee, WI Chromium oxide particles (Cr₂O₃) Obtained fromAldrich, Milwaukee, WI

Example 21

[0194] About 25 grams of the beads from Example 1 were placed in agraphite die and hot-pressed using uniaxial pressing apparatus (obtainedunder the trade designation “HP-50”, Thermal Technology Inc., Brea,Calif.). The hot-pressing was carried out in an argon atmosphere and13.8 megapascals (MPa) (2000 pounds per square inch or 2 ksi) pressure.The hot-pressing furnace was ramped up to 970° C., at 25° C./minute. Theresult was a disc, 3.4 cm in diameter and 0.6 cm thick, of transparentbulk material. A DTA trace was conducted as described in Example 1-20.The trace exhibited an endothermic event at temperature around 885° C.,as evidenced by the downward change in the curve of the trace. It isbelieved this event was due to the glass transition (T_(g)) of the glassmaterial. The same material exhibited an exothermic event at atemperature around 928° C., as evidenced by the sharp peak in the trace.It is believed that this event was due to the crystallization (T_(x)) ofthe material.

Example 22

[0195] A 250-ml polyethylene bottle (7.3-cm diameter) was charged withthe following 50-gram mixture: 19.3 grams of alumina particles (obtainedfrom Alcoa Industrial Chemicals, Bauxite, Ark., under the tradedesignation “Al6SG”), 9.5 grams of zirconium oxide particles (obtainedfrom Zirconia Sales, Inc. of Marietta, Ga. under the trade designation“DK-2”), and 21.2 grams of lanthanum oxide particles (obtained fromMolycorp Inc., Mountain Pass, Calif.), 75 grams of isopropyl alcohol,and 200 grams of alumina milling media (cylindrical in shape, bothheight and diameter of 0.635 cm; 99.9% alumina; obtained from Coors,Golden, Colo.). The contents of the polyethylene bottle were milled for16 hours at 60 revolutions per minute (rpm). The ratio of alumina tozirconia in the starting material was 2:1, and the alumina and zirconiacollectively made up about 58 weight percent (wt-%). After the milling,the milling media were removed and the slurry was poured onto a warm(approximately 75° C.) glass (“PYREX”) pan and dried. The dried mixturewas screened through a 70-mesh screen (212-micrometer opening size) withthe aid of a paint brush.

[0196] After grinding and screening, the mixture of milled feedparticles was fed slowly (0.5 gram/minute) into a hydrogen/oxygen torchflame to melt the particles. The torch used to melt the particles,thereby generating molten droplets, was a Bethlehem bench burner PM2DModel B obtained from Bethlehem Apparatus Co., Hellertown, Pa. Hydrogenand oxygen flow rates for the torch were as follows. For the inner ring,the hydrogen flow rate was 8 standard liters per minute (SLPM) and theoxygen flow rate was 3.5 SLPM. For the outer ring, the hydrogen flowrate was 23 SLPM and the oxygen flow rate was 12 SLPM. The dried andsized particles were fed slowly (0.5 gram/minute) into the torch flame,which melted the particles and carried them on to an inclined stainlesssteel surface (approximately 51 centimeters (20 inches) wide with aslope angle of 45 degrees) with cold water running over (approximately 8liters/minute) the surface to rapidly quench the molten droplets. Theresulting molten and quenched beads were collected and dried at 110° C.The particles were spherical in shape and varied in size from a fewmicrometers (i.e., microns) up to 250 micrometers.

[0197] Subsequently, the flame-formed beads having diameters less than125 micrometers were then passed through a plasma gun and deposited onstainless steel substrates as follows.

[0198] Four 304 stainless steel substrates (76.2 millimeter (mm)×25.4mm×3.175 mm dimensions), and two 1080 carbon steel substrates (76.2mm×25.4 mm×1.15 mm) were prepared in the following manner. The sides tobe coated were sandblasted, washed in an ultrasonic bath, and then wipedclean with isopropyl alcohol. Four stainless steel and one 1080 carbonsteel substrates were placed approximately 10 centimeters (cm) in frontof the nozzle of a plasma gun (obtained under the trade designation“Praxair SG-100 Plasma Gun” from Praxair Surface Technologies, Concord,N.H.). The second 1080 carbon steel was placed 18 cm in front of thenozzle of the plasma gun. The coatings made on the second 1080 carbonsteel samples at a distance of 18 cm in front of the nozzle of theplasma gun were not further characterized.

[0199] The plasma unit had a power rating of 40 kW. The plasma gas wasargon (50 pounds per square inch (psi), 0.3 megapascal (MPa)) withhelium as the auxiliary gas (150 psi, 1 MPa). The beads were passedthrough the plasma gun by using argon as the carrier gas (50 psi, 0.3MPa) using a Praxair Model 1270 computerized powder feeder (obtainedfrom Praxair Surface Technologies, Concord, N.H.). During deposition, apotential of about 40 volts and a current of about 900 amperes wasapplied and the plasma gun was panned left to right, up and down, toevenly coat the substrates. When the desired thickness was achieved, theplasma spray was shut off and the samples were recovered. The 1080carbon steel substrate was flexed, thus separating the coating from thesubstrate resulting in a free-standing bulk material. The depositedmaterial had a z dimension (thickness) of about 1350 micrometers, asdetermined using optical microscopy.

[0200] The phase composition (glassy/amorphous/crystalline) wasdetermined through Differential Thermal Analysis (DTA) as describedbelow. The material was classified as amorphous if the corresponding DTAtrace of the material contained an exothermic crystallization event(T_(x)). If the same trace also contained an endothermic event (T_(g))at a temperature lower than T_(x) it was considered to consist of aglass phase. If the DTA trace of the material contained no such events,it was considered to contain crystalline phases.

[0201] Differential thermal analysis (DTA) was conducted using thefollowing method. DTA runs were made (using an instrument obtained fromNetzsch Instruments, Seib, Germany under the trade designation “NETZSCHSTA 409 DTA/TGA”) using a −140+170 mesh size fraction (i.e., thefraction collected between 105-micrometer opening size and 90-micrometeropening size screens). The amount of each screened sample placed in a100-microliter Al₂O₃ sample holder was about 400 milligrams. Each samplewas heated in static air at a rate of 10° C./minute from roomtemperature (about 25° C.) to 1100° C.

[0202] The coated material (on 304 stainless steel substrates) exhibitedan endothermic event at a temperature around 880° C., as evidenced by adownward change in the curve of the trace. It is believed this event wasdue to the glass transition (T_(g)) of the glass material. The samematerial exhibited an exothermic event at a temperature around 931° C.,as evidenced by a sharp peak in the trace. It is believed that thisevent was due to the crystallization (T_(x)) of the material. Thus, thecoated material (on 304 stainless steel substrates) and thefree-standing bulk material were glassy as determined by a DTA trace.

[0203] A portion of the glassy free-standing bulk material was thenheat-treated at 1300° C. for 48 hours. Powder X-ray diffraction, XRD,(using an X-ray diffractometer (obtained under the trade designation“PHILLIPS XRG 3100” from Phillips, Mahwah, N.J.) with copper K □1radiation of 1.54050 Angstrom)) was used to determine the phasespresent. The phases were determined by comparing the peaks present inthe XRD trace of the crystallized material to XRD patterns ofcrystalline phases provided in JCPDS (Joint Committee on PowderDiffraction Standards) databases, published by International Center forDiffraction Data. The resulting crystalline material included LaAIO₃,ZrO₂ (cubic, tetragonal), LaAl₁₁O₁₈, and transitional Al₂O₃ phases.

[0204] Another portion of the glassy free-standing bulk material wascrystallized at 1300° C. for 1 hour in an electrically heated furnace(obtained from CM Furnaces, Bloomfield, N.J. under the trade designation“Rapid Temp Furnace”). The crystallized coating was crushed with ahammer into particles of −30+35 mesh size (i.e., the fraction collectedbetween 600-micrometer opening size and 500-micrometer opening sizescreens). The particles were cleaned of debris by washing in a sonicbath (obtained from Cole-Parmer, Vernon Hills, Ill., under the tradedesignation “8891”) for 15 minutes, dried at 100° C., and several weremounted on a metal cylinder (3 cm in diameter and 2 cm high) usingcarbon tape. The mounted sample was sputter coated with a thin layer ofgold-palladium and viewed using a JEOL scanning electron microscopy(SEM) (Model JSM 840A). The fractured surface was rough and no crystalscoarser than 200 nanometers (nm) were observed (FIG. 5) in the SEM.

Example 23

[0205] Feed particles were made as described in Example 22 using thefollowing 50-gram mixture: 21.5 grams of alumina particles (obtainedfrom Alcoa Industrial Chemicals, Bauxite, Ark. under the tradedesignation “A16SG”), 9 grams of zirconium oxide particles (obtainedfrom Zirconia Sales, Inc. of Marietta, Ga. under the trade designation“DK-2”), and 19.5 grams of cerium oxide particles (obtained fromRhone-Poulence, France). The ratio of alumina to zirconia in thestarting material was 2.4:1 and the alumina and zirconia collectivelymade up about 61 weight percent. Feed particles were flame-formed intobeads (of a size that varied from a few micrometers up to 250micrometers) as described in Example 22. Subsequently, the flame-formedbeads having diameters between 180 micrometers and 250 micrometers werepassed through a plasma gun and deposited on stainless and carbon steelsubstrates as described in Example 22.

[0206] The 1080 carbon steel substrates were flexed, thus separating thecoating from the substrate resulting in a free-standing bulk material.The resulting bulk material had a z dimension (thickness) of about 700micrometers, as determined using optical microscopy. The microstructurewas also observed using optical microscopy. The material consisted ofgenerally spherical and oblique crystalline particles, which wereopaque, within a predominantly amorphous matrix, which was transparent.Amorphous material is typically transparent due to the lack of lightscattering centers such as crystal boundaries, while the crystallineparticles show a crystalline structure and are opaque due to lightscattering effects. The crystalline phases, determined by powder XRDanalysis as described in Example 22, consisted of Zr₀ ₄Ce₀ ₆O₂ (cubic)and transitional Al₂O₃.

[0207] A second deposition experiment was carried out using theflame-formed beads having diameters less than 125 micrometers. Theresulting coating had a z dimension (thickness) of about 1100micrometers, as determined using optical microscopy. The microstructurewas also observed using optical microscopy. This material had similarfeatures (i.e., consisted of generally spherical and oblique crystallineparticles within a predominantly amorphous matrix) to those of thematerial formed from beads having diameters between 180 micrometers and250 micrometers. The crystalline phases, determined by XRD analysis asdescribed in Example 22, consisted of Zr_(0.4)Ce₀ ₆O₂ (cubic) andtransitional Al₂O₃.

[0208] The average hardness of the as-sprayed material of this examplewas determined as follows. Sections of the material were mounted inmounting resin (obtained under the trade designation “TRANSOPTIC POWDER”from Buehler, Lake Bluff, Ill.). The resulting cylinder of resin wasabout 2.5 cm in diameter and about 1.9 cm high. The mounted section wasprepared using conventional polishing techniques using a polisher(obtained from Buehler, Lake Bluff, Ill. under the trade designation“ECOMET 3”). The sample was polished for about 3 minutes with a diamondwheel, followed by 5 minutes of polishing with each of 45, 30, 15, 9, 3,and 1-micrometer slurries. The microhardness measurements were madeusing a conventional microhardness tester (obtained under the tradedesignation “MITUTOYO MVK-VL” from Mitutoyo Corporation, Tokyo, Japan)fitted with a Vickers indenter using a 100-gram indent load. Themicrohardness measurements were made according to the guidelines statedin ASTM Test Method E384 Test Methods for Microhardness of Materials(1991), the disclosure of which is incorporated herein by reference. Theaverage microhardness (an average of 20 measurements) of the material ofthis example was 15 gigapascals (Gpa).

Example 24

[0209] Feed particles were made as described in Example 22 using thefollowing 50-gram mixture: 27.9 grams of alumina particles (obtainedfrom Alcoa Industrial Chemicals, Bauxite, Ark. under the tradedesignation “A16SG”), 7.8 grams of zirconium oxide particles (obtainedfrom Zirconia Sales, Inc. of Marietta, Ga. under the trade designation“DK-2”), and 14.3 grams of yttrium oxide particles (obtained from H. C.Stark Newton, Mass.). The ratio of alumina to zirconia of initialstarting materials was 3.5:1 and the alumina and zirconia collectivelymade up about 72 weight percent. The feed particles were then screenedthrough a 30-mesh screen (600-micrometer opening size) and heat-treatedat 1400° C. for 2 hours in an electrically heated furnace (obtained fromCM Furnaces, Bloomfield, N.J. under the trade designation “Rapid TempFurnace”). The heat-treated particles were further screened to separateout particles with diameters between 125 micrometers and 180micrometers, which were then passed through a plasma gun and depositedon stainless steel substrates as described in Example 22.

[0210] The 1080 carbon steel substrate was flexed, thus separating thecoating from the substrate resulting in a free-standing bulk material.The resulting bulk material had a z dimension (thickness) of about 700micrometers, as determined using optical microscopy. The microstructurewas observed using optical microscopy. This material consisted ofgenerally crystalline opaque particles (which retained their originalshapes) within a predominantly transparent, amorphous matrix. Thecrystalline phases, determined by powder XRD analysis as described inExample 22, consisted of Al₅Y₃O₁₂ and Y_(0.15)Zr_(0.85)O_(1.93).

[0211] Another portion of the free-standing bulk material wascrystallized at 1300° C. for 1 hour and the fractured surface wassputter coated with a thin layer of gold-palladium and viewed using aJEOL SEM (Model JSM 840A), as described above in Example 22. Thefractured surface was rough and no crystals coarser than 200 nm wereobserved (FIG. 6).

[0212] A second deposition experiment was carried out using heat-treatedparticles having diameters less than 125 micrometers. The resultingcoating was about 1500 micrometers thick (z dimension). Themicrostructure was observed using optical microscopy. This material hadsimilar features (consisted of generally opaque, crystalline particles(which retained their original shapes) within a predominantlytransparent, amorphous matrix) to the material formed from beads havingdiameters between 180 micrometers and 250 micrometers. The crystallinephases, determined by XRD analysis as described in Example 22, consistedof Al₅Y₃O₁₂ and Y_(0.15)Zr_(0.85)O_(1.93).

Example 25

[0213] A thick coating consisting of various layers of the above threeexamples was plasma sprayed using feed particles produced in Examples22-24. The first layer was coated as described in Example 23, the secondas described in Example 22, and the third as described in Example 24.

[0214] The substrate was not sandblasted prior to coating so that it wasremoved easily by plying it apart by hand, resulting in a free-standingbulk material, approximately 75 millimeters (mm)×25 mm×7.5 mm. Across-section, cutting through each layer, was sectioned from thematerial using a diamond saw. The sectioned piece was mounted inmounting resin (obtained under the trade designation “TRANSOPTIC POWDER”from Buehler, Lake Bluff, Ill.) such that the different layers werevisible. The resulting cylinder of resin was about 2.5 cm in diameterand about 1.9 cm tall (i.e., high). The mounted section was preparedusing conventional polishing techniques using a polisher (obtained fromBuehler, Lake Bluff, Ill. under the trade designation “ECOMET 3”). Thesample was polished for about 3 minutes with a diamond wheel, followedby 5 minutes of polishing with each of 45, 30, 15, 9, 3, and1-micrometer slurries.

[0215] The first layer had a z dimension (thickness) of approximately2.5 mm, as determined using optical microscopy. The microstructure wasobserved using optical microscopy. This material had similar features tothose of the material of Example 23 (i.e., consisted of generallyspherical and opaque crystalline particles within a predominantlytransparent, amorphous matrix). The second layer had a z dimension(thickness) of approximately 2 mm, as determined using opticalmicroscopy. The microstructure was also observed using opticalmicroscopy. This material had similar features to those of the materialof Example 22 (i.e., was transparent suggesting it was amorphous). Thethird layer had a z dimension (thickness) of approximately 3 mm, asdetermined using optical microscopy. The microstructure was alsoobserved using optical microscopy. This material had similar features tothose of the material of Example 24 (i.e., it consisted of generallyopaque crystalline particles (which retained their original shapes)within a predominantly transparent, amorphous matrix).

Example 26

[0216] The consolidated material produced in Example 21 was crushed byusing a “Chipmunk” jaw crusher (Type VD, manufactured by BICO Inc.,Burbank, Calif.) into abrasive particles and graded to retain the −30+35mesh fraction (i.e., the fraction collected between 600-micrometeropening size and 500-micrometer opening size screens) and the −35+40mesh fraction (i.e., the fraction collected between 500-micrometeropening size and 425-micrometer opening size screens). The two meshfractions were combined to provide a 50/50 blend.

[0217] An average aspect ratio of the particles was measured using aZeiss Image Analysis System (Zeiss Stemi SV11 microscope and softwareloaded on a computer) and a video camera (3 CCD camera, model 330,(obtained from Dage MTI Inc., Michigan City, Ind.)). The resultingaspect ratio was 1.86.

[0218] Density of the particles was measured using a gas pychometerAccuPyc 1330, Micromeritics, Norcross, Ga. The resulting density was4.65 grams per cubic centimeter (g/cc).

[0219] The crushed particles were heat-treated at 1300° C. for 45minutes in an electrically heated furnace (obtained from CM Furnaces,Bloomfield, N.J. under the trade designation “Rapid Temp Furnace”). Theresulting crystalline particles retained their original crushed shape.The density of the particle was found to be 5.24 grams per cubiccentimeter (g/cc). The crystallized glass ceramic phases, determined byXRD analysis as described in Examples 22, were composed of LaAIO₃,cubic/tetragonal ZrO₂, LaAl₁₁O₁₈, α-Al₂O₃, monoclinic ZrO₂ and minoramorphous phases.

Example 27-28

[0220] A 250-ml polyethylene bottle (7.3-cm diameter) was charged with19.3 grams of alumina particles (obtained from Alcoa IndustrialChemicals, Bauxite, Ark., under the trade designation “Al6SG”), 9.5grams of zirconium oxide particles (obtained from Zirconia Sales, Inc.of Marietta, Ga. under the trade designation “DK-2”), and 21.2 grams oflanthanum oxide particles (obtained from Molycorp Inc., Mountain Pass,Calif.), 75 grams of isopropyl alcohol, and 200 grams of alumina millingmedia (cylindrical shape, both height and diameter of 0.635 cm; 99.9%alumina; obtained from Coors, Golden, Colo.). The contents of thepolyethylene bottle were milled for 16 hours at 60 revolutions perminute (rpm). After the milling, the milling media were removed and theslurry was poured onto a warm (approximately 75° C.) glass (“PYREX”)pan, where it dried within 3 minutes. The dried mixture was screenedthrough a 14-mesh screen (1400 micrometer opening size) with the aid ofa paint brush and pre-sintered at 1400° C., in air, for two hours.

[0221] A hole (approximately 13 mm in diameter, about 8 cm deep) wasbored at the end of a graphite rod (approximately 60 cm long, 15 mm indiameter). About 20 grams of pre-sintered particles were inserted intothe hollow end. The hollow end of the graphite rod was inserted into thehot zone of a resistively heated furnace (obtained from AstroIndustries, Santa Barbara, Calif.). The furnace was modified to convertit into a tube furnace with graphite tube with an inner diameter ofapproximately 18 mm. The hot zone was maintained at a temperature of2000° C. and the furnace was tilted approximately 30° so that the meltwould not spill out of the rod. The rod end was held in the hot zone for10 minutes to ensure uniform melting. After the ten minutes, the rod wasquickly removed from the furnace and tilted to pour the melt onto aquenching surface.

[0222] For Example 27, the quenching surface was two opposing stainlesssteel plates. The plates, 17.8 cm×5 cm×2.5 cm, were placed on their longedges parallel to each other with a gap of about 1 mm. The melt waspoured into the gap where it rapidly solidified into a plate with a zdimension (thickness) of about 1 mm. The quenched melt was predominantlytransparent and amorphous and exhibited a glass transition (T_(g)) of885° C. and a crystallization temperature (T_(x)) of 930° C. asdetermine by a DTA trace obtained as described in Examples 1-20.

[0223] For Example 28, the quenching surface was two counter-rotatingsteel rollers. Rollers were 5 cm in diameter and driven by an electricmotor at 80 rpm. The gap between the rollers was approximately 0.8 mm.The melt was poured into the gap where the rollers rapidly solidifiedinto a plate with significant x and y dimensions and a z dimension(thickness) of 0.8 mm. The quenched melt was predominantly transparentand amorphous and exhibited a glass transition (T_(g)) of 885° C. and acrystallization temperature (T_(x)) of 930° C., as determine by a DTAtrace obtained as described in Examples 1-20.

Example 29

[0224] The bulk amorphous/glass material produced in Example 21 wascrushed by using a “Chipmunk” jaw crusher (Type VD, manufactured by BICOInc., Burbank, Calif.) into abrasive particles and graded to retain the−30+35 mesh fraction (i.e., the fraction collected between600-micrometer opening size and 500-micrometer opening size screens) andthe −35+40 mesh fraction (i.e., the fraction collected between500-micrometer opening size and 425-micrometer opening size screens).The two mesh fractions were combined to provide a 50/50 blend.

[0225] An aspect ratio measurement was taken using the method describedin Example 26. The resulting aspect ratio was 1.83.

[0226] Density of the particles was taken using the method described inExample 26. The resulting density was 4.61 g/cc.

Examples 30-31

[0227] A hot-pressed disk was prepared as describe in Example 21 and wassectioned into 2 bars (approximately 2 cm×0.5 cm×0.5 cm) using a diamondsaw (obtained from Buehler, Lake Bluff, Ill. under the trade designation“ISOMET 1000”). Both bars were annealed in an electrically heatedfurnace (obtained from CM Furnaces, Bloomfield, N.J. under the tradedesignation “Rapid Temp Furnace”) at 800° C. for 2 hours. Nocrystallization occurred during the annealing process.

[0228] For Example 30, one bar was crushed with a hammer into particlesof −30+35 mesh size (i.e., the fraction collected between 600-micrometeropening size and 500-micrometer opening size screens). The crushedparticles were heat-treated at 1300° C. for 1 hour in an electricallyheated furnace (obtained from CM Furnaces, Bloomfield, N.J. under thetrade designation “Rapid Temp Furnace”) to crystallize them. Theparticles were cleaned of debris by washing in a sonic bath (obtainedfrom Cole-Parmer, Vernon Hills, Ill., under the trade designation“8891”) for 15 minutes, dried at 100° C., and several were mounted on ametal cylinder (3 cm in diameter and 2 cm high) using carbon tape. Themounted sample was sputtered with a thin layer of gold-palladium andview using a JEOL SEM (Model JSM 840A).

[0229] Classic glass fracture characteristics were noticeable in thematerial of Example 30, even after crystallization took place. Thefracture surface shown in FIG. 7 is a good example of Wallner lines,common in most glass fracture. The fracture surface shown in FIG. 8displays hackle, another common characteristic of glass fracture. Thedefinitions of Wallner lines and hackle are taken as those given in thetextbook, Fundamentals of Inorganic Glasses, Arun K Varshneya, p.425-27, 1994.

[0230] The average hardness of the material of Example 30 was determinedas follows. Several particles were mounted in mounting resin (obtainedunder the trade designation “TRANSOPTIC POWDER” from Buehler, LakeBluff, Ill.). The resulting cylinder of resin was about 2.5 cm indiameter and about 1.9 cm high. The mounted section was prepared usingconventional polishing techniques using a polisher (obtained fromBuehler, Lake Bluff, Ill. under the trade designation “ECOMET 3”). Thesample was polished for about 3 minutes with a diamond wheel, followedby 5 minutes of polishing with each of 45, 30, 15, 9, 3 and 1-micrometerslurries. The microhardness measurements were made using a conventionalmicrohardness tester (obtained under the trade designation “MITUTOYOMVK-VL” from Mitutoyo Corporation, Tokyo, Japan) fitted with a Vickersindenter using a 500-gram indent load. The microhardness measurementswere made according to the guidelines stated in ASTM Test Method E384Test Methods for Microhardness of Materials (1991), the disclosure ofwhich is incorporated herein by reference. The microhardness were anaverage of 20 measurements. The average microhardness of the material ofExample 30 was 16.4 GPa.

[0231] For Example 31, the second half of the bar was heat-treated at1300° C. for 1 hour in an electrically heated furnace (obtained from CMFurnaces, Bloomfield, N.J. under the trade designation “Rapid TempFurnace”). The heat-treated bar was crushed with a hammer into particlesof −30+35 mesh size (i.e., the fraction collected between 600-micrometeropening size and 500-micrometer opening size screens). The particleswere mounted and viewed using above described methods.

[0232] In contrast to the glass-fractured surface of the material ofExample 30, the material of Example 31 exhibited fractured surfacescommonly seen in polycrystalline material. The fractured surface shownin FIG. 9 shows a rough surface with feature similar in size to thecrystal size, typical of transgranular fracture.

Example 32

[0233] Beads from Example 4 were heat-treated at 1300° C. for 30 minutesin an electrically heated furnace. The crystallized beads were mountedand polished as described in Examples 30-31 and coated with a thin layerof gold-palladium and view using a JEOL SEM (Model JSM 840A). FIG. 10 isa typical back-scattered electron (BSE) micrograph of the microstructurefound in crystallized beads. The crystallized sample was nanocrystallinewith very narrow distribution of crystal size, with no crystals beinglarger than 200 nm visually observed from the micrograph.

[0234] The average crystal size was determined by the line interceptmethod according to the ASTM standard E 112-96 “Standard Test Methodsfor Determining Average Grain Size”. The sample was mounted in mountingresin (obtained under the trade designation “TRANSOPTIC POWDER” fromBuehler, Lake Bluff, Ill.). The resulting cylinder of resin was about2.5 cm in diameter and about 1.9 cm high. The mounted section wasprepared using conventional polishing techniques using a polisher(obtained from Buehler, Lake Bluff, Ill. under the trade designation“ECOMET 3”). The sample was polished for about 3 minutes with a diamondwheel, followed by 5 minutes of polishing with each of 45, 30, 15, 9, 3,and 1-micrometer slurries. The mounted and polished sample was coatedwith a thin layer of gold-palladium and view using a JEOL SEM (Model JSM840A). A typical back-scattered electron (BSE) micrograph of themicrostructure found in the sample was used to determine the averagecrystal size as follows. The number of crystals that intersected perunit length (NL) of a random line were drawn across the micrograph wascounted. The average crystal size is determined from this number usingthe following equation.${{Average}\quad {Crystal}\quad {Size}} = \frac{1.5}{N_{L}M}$

[0235] Where N_(L) is the number of crystals intersected per unit lengthand M is the magnification of the micrograph. The average crystal sizein the sample was 140 nm, as measured by line-intercept method.

Example 33

[0236] The consolidated material produced in Example 21 was heat treatedat 1300° C. for 45 minutes in an electrically heated furnace (obtainedfrom CM Furnaces, Bloomfield, N.J. under the trade designation “RapidTemp Furnace”). The resulting crystalline material was crushed by usinga “Chipmunk” jaw crusher (Type VD, manufactured by BICO Inc., Burbank,Calif.) into abrasive particles and graded to retain the −30+35 fraction(i.e., the fraction collected between 600-micrometer opening size and500-micromter opening size screens) and the −35+40 mesh fraction (i.e.,the fraction collected 500-micrometer opening size and 5425-micrometeropening size screens). The two mesh fractions were combined to provide a50/50 blend.

[0237] An aspect ratio measurement was taken using the method of Example26. The resulting aspect ratio was 1.84.

[0238] Density of the particles was taken using the method of Example26. The resulting density was 5.19 g/cc.

Example 34

[0239] About 150 grams of the beads prepared as described in Example 1were placed in a 5 centimeter (cm)×5 cm×5 cm steel can, which was thenevacuated and sealed from the atmosphere. The steel can was subsequentlyhot-isostatically pressed (HIPed) using a HIP apparatus (obtained underthe trade designation “IPS Eagle-6”, American Isostatic Pressing, OH).The HIPing was carried out at 207 MPa (30 ksi) pressure in an argonatmosphere. The HIPing furnace was ramped up to 970° C. at 25° C./minuteand held at that temperature for 30 minutes. After the HIPing, the steelcan was cut and the charge material removed. It was observed that beadscoalesced into a chunk of transparent, glassy material. The DTA trace,conducted as described in Examples 1-20, exhibited a glass transition(T_(g)) of 879° C. and a crystallization temperature (T_(x)) of 931° C.

Example 35

[0240] A polyethylene bottle was charged with 27.5 grams of aluminaparticles (obtained under the trade designation “APA-0.5” from CondeaVista, Tucson, Ariz.), 22.5 grams of calcium oxide particles (obtainedfrom Alfa Aesar, Ward Hill, Mass.) and 90 grams of isopropyl alcohol.About 200 grams of zirconia milling media (obtained from Tosoh Ceramics,Division of Bound Brook, N.J., under “YTZ” designation) were added tothe bottle, and the mixture was milled at 120 revolutions per minute(rpm) for 24 hours. After the milling, the milling media were removedand the slurry was poured onto a glass (“PYREX”) pan where it was driedusing a heat-gun. The dried mixture was ground with a mortar and pestleand screened through a 70-mesh screen (212-micrometer opening size).

[0241] After grinding and screening, some of the particles were fed intoa hydrogen/oxygen torch flame. The torch used to melt the particles,thereby generating melted glass beads, was a Bethlehem bench burner PM2Dmodel B, obtained from Bethlehem Apparatus Co., Hellertown, Pa.,delivering hydrogen and oxygen at the following rates. For the innerring, the hydrogen flow rate was 8 standard liters per minute (SLPM) andthe oxygen flow rate was 3 SLPM. For the outer ring, the hydrogen flowrate was 23 (SLPM) and the oxygen flow rate was 9.8 SLPM. The dried andsized particles were fed directly into the torch flame, where they weremelted and transported to an inclined stainless steel surface(approximately 51 centimeters (cm) (20 inches) wide with the slope angleof 45 degrees) with cold water running over (approximately 8liters/minute) the surface to form amorphous beads.

Examples 36-39

[0242] Examples 36-39 glass beads were prepared as described in Example35, except the raw materials and the amounts of raw materials used arelisted in Table 3, below, and the milling of the raw materials wascarried out in 90 (milliliters) ml of isopropyl alcohol with 200 gramsof the zirconia media (obtained from Tosoh Ceramics, Division of BoundBrook, N.J., under “YTZ” designation) at 120 rpm for 24 hours. Thesources of the raw materials used are listed in Table 4, below. TABLE 3Example Weight percent of components Batch amounts, g 36 CaO: 36 CaO: 18Al₂O₃: 44 Al₂O₃: 22 ZrO₂: 20 ZrO₂: 10 37 La₂O₃: 48 La₂O₃: 24 Al₂O₃: 52Al₂O₃: 26 38 La₂O₃: 40.9 La₂O₃: 20.45 Al₂O₃: 40.98 Al₂O₃: 20.49 ZrO₂:18.12 ZrO₂: 9.06 39 SrO: 22.95 SrO: 11.47 Al₂O₃: 62.05 Al₂O₃: 31.25ZrO₂: 15 ZrO₂: 7.5

[0243] TABLE 4 Raw Material Source Alumina particles (Al₂O₃) Obtainedfrom Condea Vista, Tucson, AZ under the trade designation “APA-0.5”Calcium oxide particles (CaO) Obtained from Alfa Aesar, Ward Hill, MALanthanum oxide particles Obtained from Molycorp Inc. (La₂O₃) Strontiumoxide particles Obtained from Alfa Aesar (SrO) Yttria-stabilizedObtained from Zirconia Sales, Inc. of zirconium oxide Marietta, GA underthe trade designation particles (Y-PSZ) “HSY-3”

[0244] Various properties/characteristics of some of Examples 35-39materials were measured as follows. Powder X-ray diffraction (using anX-ray diffractometer (obtained under the trade designation “PHILLIPS XRG3100” from PHILLIPS, Mahwah, N.J.) with copper K α1 radiation of 1.54050Angstrom)) was used to qualitatively measure phases present in examplematerials. The presence of a broad diffused intensity peak was taken asan indication of the amorphous nature of a material. The existence ofboth a broad peak and well-defined peaks was taken as an indication ofexistence of crystalline matter within an amorphous matrix. Phasesdetected in various examples are reported in Table 5, below. TABLE 5Phases detected via Hot-pressing Example X-ray diffraction Color T_(g),° C. T_(x), ° C. temp, ° C. 35 Amorphous* Clear 850 987 985 36Amorphous* Clear 851 977 975 37 Amorphous* Clear 855 920 970 38Amorphous* Clear 839 932 965 39 Amorphous* Clear 875 934 975

[0245] For differential thermal analysis (DTA), a material was screenedto retain glass beads within the 90-125 micrometer size range. DTA runswere made (using an instrument obtained from Netzsch Instruments, Selb,Germany under the trade designation “NETZSCH STA 409 DTA/TGA”). Theamount of each screened sample placed in a 100-microliter Al₂O₃ sampleholder was 400 milligrams. Each sample was heated in static air at arate of 10° C./minute from room temperature (about 25° C.) to 1200° C.

[0246] Referring to FIG. 11, line 345 is the plotted DTA data for theExample 35 material. Referring to FIG. 11 line 345, the materialexhibited an endothermic event at a temperature around 799° C., asevidenced by the downward curve of line 375. It was believed that thisevent was due to the glass transition (T_(g)) of the material. At about875° C., an exothermic event was observed as evidenced by the sharp peakin line 345. It was believed that this event was due to thecrystallization (T_(x)) of the material. These T_(g) and T_(x) valuesfor other examples are reported in Table 5, above.

[0247] FIGS. 12-15 are the plotted DTA data for Examples 36-39,respectively.

[0248] For each of Examples 35-39, about 25 grams of the glass beadswere placed in a graphite die and hot-pressed using uniaxial pressingapparatus (obtained under the trade designation “HP-50”, ThermalTechnology Inc., Brea, Calif.). The hot-pressing was carried out in anargon atmosphere and 13.8 megapascals (MPa) (2000 pounds per square inch(2 ksi)) pressure. The hot-pressing temperature at which appreciableglass flow occurred, as indicated by the displacement control unit ofthe hot pressing equipment described above, are reported for Examples35-39 in Table 5, above.

Examples 40-46

[0249] A polyethylene bottle was charged with the raw materials listedin Table 6, below (with the sources of the raw materials listed in Table7, below), with 90 ml of isopropyl alcohol. About 200 grams of thezirconia milling media (obtained from Tosoh Ceramics, Division of BoundBrook, N.J., under the trade designation “YTZ”) were added to thebottle, and the mixture was milled at 120 revolutions per minute (rpm)for 24 hours. After the milling, the milling media were removed and theslurry was poured onto a glass (“PYREX”) pan where it was dried using aheat-gun. The dried mixture was ground with a mortar and pestle andscreened through a 70-mesh screen (212-micrometer opening size screen).After grinding and screening, some of the particles were fed into ahydrogen/oxygen torch flame to form beads as described in Examples 1-20.TABLE 6 Example Weight percent of components Batch amounts, g 40 Y₂O₃:28.08 Y₂O₃: 14.04 Al₂O₃: 58.48 Al₂O₃: 29.24 ZrO₂: 13.43 ZrO₂: 6.72 41Y₂O₃: 19 Y₂O₃: 9.5 Al₂O₃: 51 Al₂O₃: 25.5 ZrO₂: 17.9 ZrO₂: 8.95 La₂O₃:12.1 La₂O₃: 6.05 42 Y₂O₃: 19.3 Y₂O₃: 9.65 Al₂O₃: 50.5 Al₂O₃: 25.25 ZrO₂:17.8 ZrO₂: 8.9 Nd₂O₃: 12.4 Nd₂O₃: 6.2 43 Y₂O₃: 27.4 Y₂O₃: 13.7 Al₂O₃:50.3 Al₂O₃: 25.15 ZrO₂: 17.8 ZrO₂: 8.9 Li₂CO₃: 4.5 Li₂CO₃: 2.25 44 Y₂O₃:27.4 Y₂O₃: 13.7 Al₂O₃: 50.3 Al₂O₃: 25.15 ZrO₂: 17.8 ZrO₂: 8.9 CaO: 4.5CaO: 2.25 45 Y₂O₃: 27.4 Y₂O₃: 13.7 Al₂O₃: 50.3 Al₂O₃: 25.15 ZrO₂: 17.8ZrO₂: 8.9 NaHCO₃: 2.25 NaHCO₃: 2.25 46 Y₂O₃: 27.4 Y₂O₃: 13.7 Al₂O₃: 50.3Al₂O₃: 25.15 ZrO₂: 17.8 ZrO₂: 8.9 SiO₂: 2.25 SiO₂: 2.25

[0250] TABLE 7 Raw Material Source Alumina particles (Al₂O₃) Obtainedfrom Condea Vista, Tucson, AZ under the trade designation “APA-0.5”Calcium oxide particles (CaO) Obtained from Alfa Aesar, Ward Hill, MALanthanum oxide particles Obtained from Molycorp Inc., Mountain (La₂O₃)Pass, CA Lithium carbonate particles Obtained from Aldrich Chemical Co.(Li₂CO₃) Neodymium oxide particles Obtained from Molycorp Inc. (Nd₂O₃)Silica particles (SiO₂) Obtained from Alfa Aesar Sodium bicarbonateparticles Obtained from Aldrich Chemical Co. (NaHCO₃) Yttria-stabilizedObtained from Zirconia Sales, Inc. of zirconium oxide Marietta, GA underthe trade designation particles (Y-PSZ) “HSY-3”

[0251] Various properties/characteristics of some Example 40-46materials were measured as follows. Powder X-ray diffraction (using anX-ray diffractometer (obtained under the trade designation “PHILLIPS XRG3100” from Phillips, Mahwah, N.J.) with copper K al radiation of 1.54050Angstrom)) was used to qualitatively measure phases present in examplematerials. The presence of a broad diffused intensity peak was taken asan indication of the amorphous nature of a material. The existence ofboth a broad peak and well-defined peaks was taken as an indication ofexistence of crystalline matter within an amorphous matrix. Phasesdetected in various examples are reported in Table 8, below. TABLE 8Exam- Phases detected via Hot-pressing ple X-ray diffraction ColorT_(g), ° C. T_(x), ° C. temp, ° C. 40 Amorphous* and Clear/ 874 932 980Crystalline milky 41 Amorphous* Clear 843 938 970 42 Amorphous* Blue/848 934 970 pink 43 Amorphous* Clear 821 927 970 44 Amorphous* Clear 845922 970 45 Amorphous* Clear 831 916 970 46 Amorphous* Clear 826 926 970

[0252] For differential thermal analysis (DTA), a material was screenedto retain beads in the 90-125 micrometer size range. DTA runs were made(using an instrument obtained from Netzsch Instruments, Selb, Germanyunder the trade designation “NETZSCH STA 409 DTA/TGA”). The amount ofeach screened sample placed in a 100-microliter Al₂O₃ sample holder was400 milligrams. Each sample was heated in static air at a rate of 10°C./minute from room temperature (about 25° C.) to 1200° C.

[0253] The hot-pressing temperature at which appreciable glass flowoccurred, as indicated by the displacement control unit of the hotpressing equipment described above in Examples 36-39, are reported forvarious examples in Table 8, above.

Example 47

[0254] A polyurethane-lined mill was charged with 819.6 grams of aluminaparticles (“APA-0.5”), 818 grams of lanthanum oxide particles (obtainedfrom Molycorp, Inc.), 362.4 grams of yttria-stabilized zirconium oxideparticles (with a nominal composition of 94.6 wt-% ZrO₂ (+HfO₂) and 5.4wt-% Y₂O₃; obtained under the trade designation “HSY-3” from ZirconiaSales, Inc. of Marietta, Ga.), 1050 grams of distilled water and about2000 grams of zirconia milling media (obtained from Tosoh Ceramics,Division of Bound Brook, N.J., under the trade designation “YTZ”). Themixture was milled at 120 revolutions per minute (rpm) for 4 hours tothoroughly mix the ingredients. After the milling, the milling mediawere removed and the slurry was poured onto a glass (“PYREX”) pan whereit was dried using a heat-gun. The dried mixture was ground with amortar and pestle and screened through a 70-mesh screen (212-micrometeropening size). After grinding and screening, some of the particles werefed into a hydrogen/oxygen torch flame as described in Examples 1-20.

[0255] About 50 grams of the beads was placed in a graphite die andhot-pressed using a uniaxial pressing apparatus (obtained under thetrade designation “HP-50”, Thermal Technology Inc., Brea, Calif.). Thehot-pressing was carried out at 960° C. in an argon atmosphere and 13.8megapascals (MPa) (2000 pounds per square inch (2 ksi)) pressure. Theresulting translucent disk was about 48 millimeters in diameter, andabout 5 mm thick. Additional hot-press runs were performed to makeadditional disks. FIG. 16 is an optical photomicrograph of a sectionedbar (2-mm thick) of the hot-pressed material demonstrating itstransparency.

[0256] The density of the resulting hot-pressed glass material wasmeasured using Archimedes method, and found to be within a range ofabout 4.1-4.4 g/cm³. The Youngs' modulus (E) of the resultinghot-pressed glass material was measured using a ultrasonic test system(obtained from Nortek, Richland, Wash. under the trade designation“NDT-140”), and found to be within a range of about 130-150 GPa.

[0257] The average microhardnesses of the resulting hot-pressed materialwas determined as follows. Pieces of the hot-pressed material (about 2-5millimeters in size) were mounted in mounting resin (obtained under thetrade designation “EPOMET” from Buehler Ltd., Lake Bluff, Ill.). Theresulting cylinder of resin was about 2.5 cm (1 inch) in diameter andabout 1.9 cm (0.75 inch) tall (i.e., high). The mounted samples werepolished using a conventional grinder/polisher (obtained under the tradedesignation “EPOMET” from Buehler Ltd.) and conventional diamondslurries with the final polishing step using a 1-micrometer diamondslurry (obtained under the trade designation “METADI” from Buehler Ltd.)to obtain polished cross-sections of the sample.

[0258] The microhardness measurements were made using a conventionalmicrohardness tester (obtained under the trade designation “MITUTOYOMVK-VL” from Mitutoyo Corporation, Tokyo, Japan) fitted with a Vickersindenter using a 500-gram indent load. The microhardness measurementswere made according to the guidelines stated in ASTM Test Method E384Test Methods for Microhardness of Materials (1991), the disclosure ofwhich is incorporated herein by reference. The microhardness values werean average of 20 measurements. The average microhardness of thehot-pressed material was about 8.3 GPa.

[0259] The average indentation toughness of the hot-pressed material wascalculated by measuring the crack lengths extending from the apices ofthe vickers indents made using a 500 gram load with a microhardnesstester (obtained under the trade designation “MITUTOYO MVK-VL” fromMitutoyo Corporation, Tokyo, Japan). Indentation toughness (K_(IC)) wascalculated according to the equation:

K _(IC)=0.016 (E/H)^(1/2)(P/c)^(3/2)

[0260] wherein: E=Young's Modulus of the material;

[0261] H=Vickers hardness;

[0262] P=Newtons of force on the indenter;

[0263] c=Length of the crack from the center of the indent to its end.

[0264] Samples for the toughness were prepared as described above forthe microhardness test. The reported indentation toughness values are anaverage of 5 measurements. Crack (c) were measured with a digitalcaliper on photomicrographs taken using a scanning electron microscope(“JEOL SEM” (Model JSM 6400)). The average indentation toughness of thehot-pressed material was 1.4 MPa.m^(1/2).

[0265] The thermal expansion coefficient of the hot-pressed material wasmeasured using a thermal analyser (obtained from Perkin Elmer, Shelton,Conn., under the trade designation “PERKIN ELMER THERMAL ANALYSER”). Theaverage thermal expansion coefficient was 7.6×10⁻⁶/° C.

[0266] The thermal conductivity of the hot-pressed material was measuredaccording to an ASTM standard “D 5470-95, Test Method A” (1995), thedisclosure of which is incorporated herein by reference. The averagethermal conductivity was 1.15 W/m*K.

[0267] The translucent disk of hot-pressed La₂O₃—Al₂O₃—ZrO₂ glass washeat-treated in a furnace (an electrically heated furnace (obtainedunder the trade designation “Model KKSK-666-3100” from Keith Furnaces ofPico Rivera, Calif.)) as follows. The disk was first heated from roomtemperature (about 25° C.) to about 900° C. at a rate of about 10°C./min and then held at 900° C. for about 1 hour. Next, the disk washeated from about 900° C. to about 1300° C. at a rate of about 10°C./min and then held at 1300° C. for about 1 hour, before cooling backto room temperature by turning off the furnace. Additional runs wereperformed with the same heat-treatment schedule to make additionaldisks.

[0268]FIG. 17 is a scanning electron microscope (SEM) photomicrograph ofa polished section of heat-treated Example 47 material showing the finecrystalline nature of the material. The polished section was preparedusing conventional mounting and polishing techniques. Polishing was doneusing a polisher (obtained from Buehler of Lake Bluff, Ill. under thetrade designation “ECOMET 3 TYPE POLISHER-GRINDER”). The sample waspolished for about 3 minutes with a diamond wheel, followed by threeminutes of polishing with each of 45, 30, 15, 9, and 3-micrometerdiamond slurries. The polished sample was coated with a thin layer ofgold-palladium and viewed using JEOL SEM (Model JSM 840A).

[0269] Based on powder X-ray diffraction as described in Example 22 of aportion of heat-treated Example 47 material and examination of thepolished sample using SEM in the backscattered mode, it is believed thatthe dark portions in the photomicrograph were crystalline LaAl₁₁O₁₈, thegray portions crystalline LaAlO₃, and the white portions crystallinecubic/tetragonal ZrO₂.

[0270] The density of the heat-treated material was measured usingArchimedes method, and found to be about 5.18 g/cm³. The Youngs' modulus(E) of the heat-treated material was measured using an ultrasonic testsystem (obtained from Nortek, Richland, Wash. under the tradedesignation “NDT-140”), and found to be about 260 GPa. The averagemicrohardness of the heat-treated material was determined as describedabove for the Example 47 glass beads, and was found to be 18.3 GPa. Theaverage fracture toughness (K_(IC)) of the heat-treated material wasdetermined as described above for the Example 47 hot-pressed material,and was found to be 3.3 MPa*m^(1/2).

Examples 48-62

[0271] Examples 48-62 beads were prepared as described in Example 47,except the raw materials and the amounts of raw materials, used arelisted in Table 9, below, and the milling of the raw materials wascarried out in 90 milliliters (ml) of isopropyl alcohol with 200 gramsof the zirconia media (obtained from Tosoh Ceramics, Division of BoundBrook, N.J., under the trade designation “YTZ”) at 120 rpm for 24 hours.The sources of the raw materials used are listed in Table 10, below.TABLE 9 Example Weight percent of components Batch amounts, g 48 La₂O₃:36.74 La₂O₃: 18.37 Al₂O₃: 46.98 Al₂O₃: 23.49 ZrO₂: 16.28 ZrO₂: 8.14 49La₂O₃: 35.35 La₂O₃: 17.68 Al₂O₃: 48.98 Al₂O₃: 24.49 ZrO₂: 15.66 ZrO₂:7.83 50 Al₂O₃: 41.0 Al₂O₃: 20.5 ZrO₂: 17.0 ZrO₂: 8.5 Eu₂O₃: 41.0 Eu₂O₃:20.5 51 Al₂O₃: 41.0 Al₂O₃: 20.5 ZrO₂: 18.0 ZrO₂: 9.0 Gd₂O₃: 41.0 Gd₂O₃:20.5 52 Al₂O₃: 41.0 Al₂O₃: 20.5 ZrO₂: 18.0 ZrO₂: 9.0 Dy₂O₃: 41.0 Dy₂O₃:20.5 53 La₂O₃: 35.0 La₂O₃: 17.5 Al₂O₃: 40.98 Al₂O₃: 20.49 ZrO₂: 18.12ZrO₂: 9.06 Nd₂O₃: 5.0 Nd₂O₃: 2.50 54 La₂O₃: 35.0 La₂O₃: 17.5 Al₂O₃:40.98 Al₂O₃: 20.49 ZrO₂: 18.12 ZrO₂: 9.06 CeO₂: 5.0 CeO₂: 2.50 55 La₂O₃:41.7 La₂O₃: 20.85 Al₂O₃: 35.4 Al₂O₃: 17.7 ZrO₂: 16.9 ZrO₂: 8.45 MgO: 6.0MgO: 3.0 56 La₂O₃: 43.02 La₂O₃: 21.51 Al₂O₃: 36.5 Al₂O₃: 18.25 ZrO₂:17.46 ZrO₂: 8.73 Li₂CO₃: 3.0 Li₂CO₃: 1.50 57 La₂O₃: 41.7 La₂O₃: 20.85Al₂O₃: 35.4 Al₂O₃: 17.70 ZrO₂: 16.9 ZrO₂: 8.45 Li₂CO₃: 6.0 Li₂CO₃: 3.0058 La₂O₃: 38.8 La₂O₃: 19.4 Al₂O₃: 40.7 Al₂O₃: 20.35 ZrO₂: 17.5 ZrO₂:8.75 Li₂CO₃: 3 Li₂CO₃: 1.50 59 La₂O₃: 43.02 La₂O₃: 21.51 Al₂O₃: 36.5Al₂O₃: 18.25 ZrO₂: 17.46 ZrO₂: 8.73 TiO₂: 3 TiO₂: 1.50 60 La₂O₃: 43.02La₂O₃: 21.51 Al₂O₃: 36.5 Al₂O₃: 18.25 ZrO₂: 17.46 ZrO₂: 8.73 NaHCO₃: 3.0NaHCO₃: 1.50 61 La₂O₃: 42.36 La₂O₃: 21.18 Al₂O₃: 35.94 Al₂O₃: 17.97ZrO₂: 17.19 ZrO₂: 8.60 NaHCO₃: 4.5 NaHCO₃: 2.25 62 La₂O₃: 43.02 La₂O₃:21.51 Al₂O₃: 36.5 Al₂O₃: 18.25 ZrO₂: 17.46 ZrO₂: 8.73 MgO: 1.5 MgO: 0.75NaHCO₃: 1.5 NaHCO₃: 0.75 TiO₂: 1.5 TiO₂: 0.75

[0272] TABLE 10 Raw Material Source Alumina particles (Al₂O₃) Obtainedfrom Condea Vista, Tucson, AZ under the trade designation “APA-0.5”Cerium oxide particles (CeO₂) Obtained from Rhone-Poulenc, FranceEuropium oxide particles Obtained from Aldrich Chemical Co. (Eu₂O₃)Gadolinium oxide particles Obtained from Molycorp Inc., Mountain (Gd₂O₃)Pass, CA Hafnium oxide particles Obtained from Teledyne Wah Chang (HfO₂)Albany Co., Albany, OR Lanthanum oxide particles Obtained from MolycorpInc. (La₂O₃) Lithium carbonate particles Obtained from Aldrich ChemicalCo. (Li₂CO₃) Magnesium oxide particles Obtained from Aldrich ChemicalCo. (MgO) Neodymium oxide particles Obtained from Molycorp Inc. (Nd₂O₃)Sodium bicarbonate particles Obtained from Aldrich Chemical Co. (NaHCO₃)Titanium dioxide particles Obtained from Kemira Inc., (TiO₂) Savannah,GA Yttria-stabilized zirconium Obtained from Zirconia Sales, Inc. ofoxide particles (Y-PSZ) Marietta, GA under the trade designation “HSY-3”

[0273] Various properties/characteristics of some Example 47-62materials were measured as follows. Powder X-ray diffraction (using anX-ray diffractometer (obtained under the trade designation “PHILLIPS XRG3100” from PHILLIPS, Mahwah, N.J.) with copper K α1 radiation of 1.54050Angstrom)) was used to qualitatively measure phases present in examplematerials. The presence of a broad diffused intensity peak was taken asan indication of the glassy nature of a material. The existence of botha broad peak and well-defined peaks was taken as an indication ofexistence of crystalline matter within a glassy matrix. Phases detectedin various examples are reported in Table 11, below. TABLE 11 Phasesdetected Hot- via X-ray pressing Example diffraction Color T_(g), ° C.T_(x), ° C. temp, ° C. 47 Amorphous* Clear 834 932 960 48 Amorphous*Clear 848 920 960 49 Amorphous* Clear 856 918 960 50 Amorphous* Intense874 921 975 yellow/ mustard 51 Amorphous* Clear 886 933 985 52Amorphous* Greenish 881 935 985 53 Amorphous* Blue/pink 836 930 965 54Amorphous* Yellow 831 934 965 55 Amorphous* Clear 795 901 950 56Amorphous* Clear 816 942 950 57 Amorphous* Clear 809 934 950 58Amorphous* Clear/ 840 922 950 greenish 59 Amorphous* Clear 836 934 95060 Amorphous* Clear 832 943 950 61 Amorphous* Clear 830 943 950 62Amorphous* Clear/some 818 931 950 green

[0274] For differential thermal analysis (DTA), a material was screenedto retain beads in the 90-125 micrometer size range. DTA runs were made(using an instrument obtained from Netzsch Instruments, Seib, Germanyunder the trade designation “NETZSCH STA 409 DTA/TGA”). The amount ofeach screened sample placed in a 100-microliter Al₂O₃ sample holder was400 milligrams. Each sample was heated in static air at a rate of 10°C./minute from room temperature (about 25° C.) to 1200° C.

[0275] Referring to FIG. 18, line 801 is the plotted DTA data for theExample 47 material. Referring to FIG. 18 line 801, the materialexhibited an endothermic event at temperature around 840° C., asevidenced by the downward curve of line 801. It was believed that thisevent was due to the glass transition (T_(g)) of the material. At about934° C., an exothermic event was observed as evidenced by the sharp peakin line 801. It was believed that this event was due to thecrystallization (T_(x)) of the material. These T_(g) and T_(x) valuesfor other examples are reported in Table 11, above.

[0276] The hot-pressing temperature at which appreciable glass flowoccurred, as indicated by the displacement control unit of the hotpressing equipment described above, are reported for various examples inTable 11, above.

Example 63

[0277] A polyethylene bottle was charged with 20.49 grams of aluminaparticles (“APA-0.5”), 20.45 grams of lanthanum oxide particles(obtained from Molycorp, Inc.), 9.06 grams of yttria-stabilizedzirconium oxide particles (with a nominal composition of 94.6 wt-% ZrO₂(+HfO₂) and 5.4 wt-% Y₂O₃; obtained under the trade designation “HSY-3”from Zirconia Sales, Inc. of Marietta, Ga.), and 80 grams of distilledwater. About 450 grams of alumina milling media (10 mm diameter; 99.9%alumina; obtained from Union Process, Akron, Ohio) were added to thebottle, and the mixture was milled at 120 revolutions per minute (rpm)for 4 hours to thoroughly mix the ingredients. After the milling, themilling media were removed and the slurry was poured onto a glass(“PYREX”) pan where it was dried using a heat-gun. The dried mixture wasground with a mortar and pestle and screened through a 70-mesh screen(212-micrometer opening size).

[0278] A small quantity of the dried particles was melted in an arcdischarge furnace (Model No. 5T/A 39420; from Centorr Vacuum Industries,Nashua, N.H.). About 1 gram of the dried and sized particles was placedon a chilled copper plate located inside the furnace chamber. Thefurnace chamber was evacuated and then backfilled with Argon gas at 13.8kilopascals (kPa) (2 pounds per square inch (psi)) pressure. An arc wasstruck between an electrode and a plate. The temperatures generated bythe arc discharge were high enough to quickly melt the dried and sizedparticles. After melting was complete, the material was maintained in amolten state for about 10 seconds to homogenize the melt. The resultantmelt was rapidly cooled by shutting off the arc and allowing the melt tocool on its own. Rapid cooling was ensured by the small mass of thesample and the large heat sinking capability of the water chilled copperplate. The fused material was removed from the furnace within one minuteafter the power to the furnace was turned off. Although not wanting tobe bound by theory, it is estimated that the cooling rate of the melt onthe surface of the water chilled copper plate was above 100° C./second.The fused material were transparent glass beads (largest diameter of abead was measured at 2.8 millimeters (mm)).

[0279] The resulting amorphous beads were placed in a poyethylene bottle(as in Example 1) together with 200 grams of 2-mm zirconia milling media(obtained from Tosoh Ceramics Bound Brook, N.J. under the tradedesignation “YTZ”). Three hundred grams of distilled water was added tothe bottle, and the mixture milled for 24 hours at 120 rpm to pulverizebeads into powder. The milled material was dried using a heat gun.Fifteen grams of the dried particles were placed in a graphite die andhot-pressed at 960° C. as described in Examples 21. The resulting diskwas translucent.

Example 64

[0280] Example 64 fused amorphous beads were prepared as described inExample 63. About 15 grams of the beads were hot pressed as described inExample 50except the bottom punch of the graphite die had 2 mm deepgrooves. The resulting material replicated the grooves, indicating verygood flowability of the glass during the heating under the appliedpressure.

Comparative Example A

[0281] Comparative Example A fused material was prepared as described inExample 63, except the polyethylene bottle was charged with 27 grams ofalumina particles (“APA-0.5”), 23 grams of yttria-stabilized zirconiumoxide particles (with a nominal composition of 94.6 wt-% ZrO₂ (+HfO₂)and 5.4 wt-% Y₂O₃; obtained under the trade designation “HSY-3” fromZirconia Sales, Inc. of Marietta, Ga.) and 80 grams of distilled water.The composition of this example corresponds to a eutectic composition inthe Al₂O₃-ZrO₂ binary system. The resulting 100-150 micrometers diameterspheres were partially amorphous, with significant portions ofcrystallinity as evidenced by X-ray diffraction analysis.

Example 65

[0282] A sample (31.25 grams) of amorphous beads prepared as describedin Example 47, and 18.75 grams of beads prepared as described inComparative Example A, were placed in a polyethylene bottle. After 80grams of distilled water and 300 grams of zirconia milling media (TosohCeramics, Bound Brook, N.J. under the trade designation “YTZ”) wereadded to the bottle, the mixture was milled for 24 hours at 120 rpm. Themilled material was dried using a heat gun. Twenty grams of the driedparticles were hot-pressed as described in Example 32. An SEMphotomicrograph of a polished section (prepared as described in Example47) of Example 65 material is shown in FIG. 19. The absence of crackingat interfaces between the Comparative Example A material (dark areas)and the Example 65 material (light areas) indicates the establishment ofgood bonding.

[0283] Grinding Performance of Examples 47 and 47A and ComparativeExamples B-D

[0284] Example 47 hot-pressed material was crushed by using a “Chipmunk”jaw crusher (Type VD, manufactured by BICO Inc., Burbank, Calif.) into(abrasive) particles and graded to retain the −25+30 mesh fraction(i.e., the fraction collected between 25-micrometer opening and30-micrometer opening size sieves) and −30+35 mesh fractions (i.e., thefraction collected between 30-micrometer opening size and 35-micrometeropening size sieves) (USA Standard Testing Sieves). These two meshfractions were combined to provide a 50/50 blend. The blended materialwas heat treated as described in Example 47. Thirty grams of theresulting glass-ceramic abrasive particles were incorporated into acoated abrasive disc. The coated abrasive disc was made according toconventional procedures. The glass-ceramic abrasive particles werebonded to 17.8 cm diameter, 0.8 mm thick vulcanized fiber backings(having a 2.2 cm diameter center hole) using a conventional calciumcarbonate-filled phenolic make resin (48% resole phenolic resin, 52%calcium carbonate, diluted to 81% solids with water and glycol ether)and a conventional cryolite-filled phenolic size resin (32% resolephenolic resin, 2% iron oxide,

[0285] 66% cryolite, diluted to 78% solids with water and glycol ether).The wet make resin weight was about 185 g/m². Immediately after the makecoat was applied, the glass-ceramic abrasive particles wereelectrostatically coated. The make resin was precured for 120 minutes at88° C. Then the cryolite-filled phenolic size coat was coated over themake coat and abrasive particles. The wet size weight was about 850g/m². The size resin was cured for 12 hours at 99° C. The coatedabrasive disc was flexed prior to testing.

[0286] Example 47A coated abrasive disk was prepared as described forExample 47 except the Example 47A abrasive particles were obtained bycrushing a hot-pressed and heat-treated Example 47 material, rather thancrushing then heat-treating.

[0287] Comparative Example B coated abrasive disks were prepared asdescribed for Example 47 (above), except heat-treated fused aluminaabrasive particles (obtained under the trade designation “ALODUR BFRPL””from Triebacher, Villach, Austria) was used in place of the Example 47glass-ceramic abrasive particles.

[0288] Comparative Example C coated abrasive discs were prepared asdescribed for Example 47 (above), except alumina-zirconia abrasiveparticles (having a eutectic composition of 53% Al₂O₃ and 47% ZrO₂;obtained under the trade designation “NORZON” from Norton Company,Worcester, Mass.) were used in place of the Example 47 glass-ceramicabrasive particles.

[0289] Comparative Example D coated abrasive discs were prepared asdescribed above except sol-gel-derived abrasive particles (marketedunder the trade designation “321 CUBITRON” from the 3M Company, St.Paul, Minn.) was used in place of the Example 47 glass-ceramic abrasiveparticles.

[0290] The grinding performance of Example 47 and Comparative ExamplesB-D coated abrasive discs were evaluated as follows. Each coatedabrasive disc was mounted on a beveled aluminum back-up pad, and used togrind the face of a pre-weighed 1.25 cm×18 cm×10 cm 1018 mild steelworkpiece. The disc was driven at 5,000 rpm while the portion of thedisc overlaying the beveled edge of the back-up pad contacted theworkpiece at a load of 8.6 kilograms. Each disc was used to grind anindividual workpiece in sequence for one-minute intervals. The total cutwas the sum of the amount of material removed from the workpiecesthroughout the test period. The total cut by each sample after 12minutes of grinding as well as the cut at the 12th minute (i.e., thefinal cut) are reported in Table 12, below. The Example 47 results arean average of two discs, where as one disk was tested for each ofExample 47A, and Comparative Examples B, C, and D. TABLE 12 ExampleTotal cut, g Final cut, g 47 1163 92 47A 1197 92 Comp. B 514 28 Comp. C689 53 Comp. D 1067 89

[0291] Various modifications and alterations of this invention willbecome apparent to those skilled in the art without departing from thescope and spirit of this invention, and it should be understood thatthis invention is not to be unduly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. Amorphous material comprising at least 35 percentby weight Al₂O₃, based on the total weight of the amorphous material,and a metal oxide other than Al₂O₃, wherein the amorphous materialcontains not more than 10 percent by weight collectively As₂O₃, B₂O₃,GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theamorphous material, wherein the amorphous material has x, y, and zdimensions each perpendicular to each other, and wherein each of the x,y, and z dimensions is at least 5 mm, with the proviso that if the metaloxide other than Al₂O₃ is CaO or ZrO₂, then the amorphous materialfurther comprises a metal oxide other than Al₂O₃, CaO, and ZrO₂ at leasta portion of which forms a distinct crystalline phase when the amorphousmaterial is crystallized.
 2. The amorphous material according to claim 1wherein the amorphous material does not have a T_(g).
 3. The amorphousmaterial according to claim 1 wherein the amorphous material is glass.4. The amorphous material according to claim 3 wherein the metal oxideother than Al₂O₃ is Y₂O₃.
 5. The amorphous material according to claim 3wherein the metal oxide other than Al₂O₃ is REO.
 6. An articlecomprising the amorphous material according to claim
 1. 7. Glasscomprising at least 35 percent by weight Al₂O₃, based on the totalweight of the glass, and a metal oxide other than Al₂O₃, wherein theglass contains not more than 10 percent by weight collectively As₂O₃,B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theglass, wherein the glass has x, y, and z dimensions each perpendicularto each other, and wherein each of the x, y, and z dimensions is atleast 5 mm, with the proviso that if the metal oxide other than Al₂O₃ isCaO, then the glass further comprises a metal oxide other than Al₂O₃ orCaO at least a portion of which forms a distinct crystalline phase whenthe glass is crystallized.
 8. A method for making glass-ceramic, themethod comprising: heat-treating amorphous material such that at least aportion of the amorphous material is converted to a glass-ceramic, theamorphous material comprising at least 35 percent by weight Al₂O₃, basedon the total weight of the amorphous material, and a metal oxide otherthan Al₂O₃, wherein the amorphous material contains not more than 10percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, andV₂O₅, based on the total weight of the amorphous material, wherein theamorphous material has x, y, and z dimensions each perpendicular to eachother, and wherein each of the x, y, and z dimensions is at least 5 mm,with the proviso that if the metal oxide other than Al₂O₃ is CaO orZrO₂, then the amorphous material further comprises a metal oxide otherthan Al₂O₃, CaO, and ZrO₂ at least a portion of which forms a distinctcrystalline phase when the amorphous material is crystallized.
 9. Amethod for making glass-ceramic, the method comprising: heat-treatingglass such that at least a portion of the glass is converted to aglass-ceramic, the glass comprising at least 35 percent by weight Al₂O₃,based on the total weight of the glass, and a metal oxide other thanAl₂O₃, wherein the glass contains not more than 10 percent by weightcollectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of the glass, wherein the glass has x, y, and z dimensionseach perpendicular to each other, and wherein each of the x, y, and zdimensions is at least 5 mm, with the proviso that if the metal oxideother than Al₂O₃ is CaO, then the glass further comprises a metal oxideother than Al₂O₃ or CaO at least a portion of which forms a distinctcrystalline phase when the glass is crystallized.
 10. A method formaking abrasive particles, the method comprising: heat-treatingamorphous material such that at least a portion of the amorphousmaterial is converted to a glass-ceramic, the amorphous materialcomprising at least 35 percent by weight Al₂O₃, based on the totalweight of the amorphous material, and a metal oxide other than Al₂O₃,wherein the amorphous material contains not more than 10 percent byweight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, basedon the total weight of the amorphous material, wherein the amorphousmaterial has x, y, and z dimensions each perpendicular to each other,and wherein each of the x, y, and z dimensions is at least 5 mm, withthe proviso that if the metal oxide other than Al₂O₃ is CaO or ZrO₂,then the amorphous material further comprises a metal oxide other thanAl₂O₃, CaO, and ZrO₂ at least a portion of which forms a distinctcrystalline phase when the amorphous material is crystallized; andcrushing the glass-ceramic to provide abrasive particles comprisingglass-ceramic.
 11. A method for making abrasive particles, the methodcomprising: heat-treating amorphous material such that at least aportion of the amorphous material is converted to a glass-ceramic, theamorphous material comprising at least 35 percent by weight Al₂O₃, basedon the total weight of the amorphous material, and a metal oxide otherthan Al₂O₃, wherein the amorphous material contains not more than 10percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, andV₂O₅, based on the total weight of the amorphous material, wherein theamorphous material has x, y, and z dimensions each perpendicular to eachother, and wherein each of the x, y, and z dimensions is at least 5 mm,with the proviso that if the metal oxide other than Al₂O₃ is CaO, thenthe amorphous material further comprises a metal oxide other than Al₂O₃or CaO at least a portion of which forms a distinct crystalline phasewhen the amorphous material is crystallized; and crushing theglass-ceramic to provide abrasive particles comprising theglass-ceramic.
 12. A method for making abrasive particles, the methodcomprising: heat-treating particles comprising amorphous material suchthat at least a portion of the amorphous material is converted to aglass-ceramic, the amorphous material comprising at least 35 percent byweight Al₂O₃, based on the total weight of the amorphous material ofeach particle, and a metal oxide other than Al₂O₃, wherein the amorphousmaterial contains not more than 10 percent by weight collectively As₂O₃,B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theamorphous material of each particle, wherein the amorphous material hasx, y, and z dimensions each perpendicular to each other, and whereineach of the x, y, and z dimensions is at least 5 mm, with the provisothat if the metal oxide other than Al₂O₃ is CaO or ZrO₂, then theamorphous material further comprises a metal oxide other than Al₂O₃,CaO, and ZrO₂ at least a portion of which forms a distinct crystallinephase when the amorphous material is crystallized.
 13. A method formaking abrasive particles, the method comprising: heat-treatingparticles comprising glass such that at least a portion of the glass isconverted to a glass-ceramic, the glass comprising at least 35 percentby weight Al₂O₃, based on the total weight of the glass of eachparticle, and a metal oxide other than Al₂O₃, wherein the glass containsnot more than 10 percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅,SiO₂, TeO₂, and V₂O₅, based on the total weight of the glass of eachparticle, wherein the glass has x, y, and z dimensions eachperpendicular to each other, and wherein each of the x, y, and zdimensions is at least 5 mm, with the proviso that if the metal oxideother than Al₂O₃ is CaO, then the glass further comprises a metal oxideother than Al₂O₃ or CaO at least a portion of which forms a distinctcrystalline phase when the glass is crystallized.
 14. The methodaccording to claim 13 wherein prior to the heat-treating the particlescomprising glass, a plurality of particles having a specified nominalgrade is provided, wherein at least a portion of the particles is aplurality of the particles comprising glass, and wherein theheat-treating is conducted such that a plurality of abrasive particleshaving a specified nominal grade is provided, wherein at least a portionof the abrasive particles is a plurality of the glass-ceramic abrasiveparticles.
 15. The method according to claim 13 further comprisinggrading the glass-ceramic abrasive particles to provide a plurality ofabrasive particles having a specified nominal grade, wherein at least aportion of the plurality of abrasive particles is a plurality of theglass-ceramic abrasive particles.
 16. A method for making an articlecomprising glass comprising at least 35 percent by weight Al₂O₃, basedon the total weight of the glass, and a metal oxide other than Al₂O₃,wherein the glass contains not more than 10 percent by weightcollectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, P₂O₅, TeO₂, and V₂O₅, basedon the total weight of the glass, the method comprising: providing glassparticles comprising at least 35 percent by weight Al₂O₃, based on thetotal weight of the glass, and a metal oxide other than Al₂O₃, whereinthe glass contains not more than 10 percent by weight As₂O₃, B₂O₃, GeO₂,P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of the glass, theglass having a T_(g); heating the glass particles above the T_(g) suchthat the glass particles coalesce to form a shape; and cooling the shapeto provide the article, with the proviso that if the metal oxide otherthan Al₂O₃ is CaO, then the glass further comprises a metal oxide otherthan Al₂O₃ or CaO at least a portion of which forms a distinctcrystalline phase when the glass is crystallized.
 17. A method formaking glass particles, the method comprising: atomizing a glass meltcomprising at least 35 percent by weight Al₂O₃, based on the totalweight of the glass melt, and a metal oxide other than Al₂O₃, whereinthe glass melt contains not more than 10 percent by weight collectivelyAs₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weightof the glass melt; and cooling the atomized glass melt to provide glassparticles comprising at least 35 percent by weight Al₂O₃, based on thetotal weight of each glass particle, and a metal oxide other than Al₂O₃,wherein each glass particle contains not more than 10 percent by weightcollectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of each glass particle, wherein the glass has x, y, and zdimensions each perpendicular to each other, and wherein each of the x,y, and z dimensions is at least 5 mm, with the proviso that if the metaloxide other than Al₉O₃ is CaO, then the glass further comprises a metaloxide other than Al₂O₃ or CaO at least a portion of which at least aportion of which forms a distinct crystalline phase when the glass iscrystallized.
 18. Glass-ceramic comprising at least 35 percent by weightAl₂O₃, based on the total weight of the glass-ceramic, and a metal oxideother than Al₂O₃, wherein the glass-ceramic contains not more than 10percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, andV₂O₅, based on the total weight of the glass-ceramic, wherein theglass-ceramic has x, y, and z dimensions each perpendicular to eachother, and wherein each of the x, y, and z dimensions is at least 5 mm,with the proviso that if the metal oxide other than Al₂O₃ is CaO, thenthe glass-ceramic further comprises crystals of a metal oxide other thanCaO.
 19. The glass-ceramic according to claim 18 wherein the metal oxideother than Al₂O₃ is Y₂O₃.
 20. The glass-ceramic according to claim 18wherein the metal oxide other than Al₂O₃ is REO.
 21. An articlecomprising the glass-ceramic according to claim
 18. 22. A method formaking glass-ceramic, the method comprising: heat-treating glass suchthat at least a portion of the glass is converted to a glass-ceramic,the glass comprising at least 35 percent by weight Al₂O₃, based on thetotal weight of the glass, and a metal oxide other than Al₂O₃, whereinthe glass contains not more than 10 percent by weight collectivelyAs₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weightof the glass, wherein the glass has x, y, and z dimensions eachperpendicular to each other, and wherein each of the x, y, and zdimensions is at least 5 mm, with the proviso that if the metal oxideother than Al₂O₃ is CaO or ZrO₂, then the glass further comprises ametal oxide other than Al₂O₃, CaO, and ZrO₂ at least a portion of whichforms a distinct crystalline phase when the glass is crystallized.
 23. Amethod for making a glass-ceramic article, the method comprising:providing glass particles comprising at least 35 percent by weightAl₂O₃, based on the total weight of the glass, and a metal oxide otherthan Al₂O₃, wherein the glass contains not more than 10 percent byweight As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the totalweight of the glass, the glass having a T_(g); heating the glassparticles above the T_(g) such that the glass particles coalesce to forma shape, the glass comprising at least 35 percent by weight Al₂O₃, basedon the total weight of the glass, and a metal oxide other than Al₂O₃,wherein the glass contains not more than 10 percent by weightcollectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O, based on thetotal weight of the glass, the glass having a T_(g), with the provisothat if the metal oxide other than Al₂O₃ is ZrO₂, then the glass furthercomprises at least one of Y₂O₃ or REO; cooling the shape to provide aglass article; and heat-treating the glass article to provide aglass-ceramic article.
 24. A method for making glass-ceramic particles,the method comprising: atomizing a glass melt comprising at least 35percent by weight Al₂O₃, based on the total weight of the glass melt,and a metal oxide other than Al₂O₃, wherein the glass melt contains notmore than 10 percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅,SiO₂, TeO₂, and V₂O₅, based on the total weight of the glass melt;cooling the atomized glass melt to provide glass particles comprising atleast 35 percent by weight Al₂O₃, based on the total weight of eachglass particle, and a metal oxide other than Al₂O₃, wherein the glasscontains not more than 10 percent by weight collectively As₂O₃, B₂O₃,GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of eachglass particle, wherein the glass has x, y, and z dimensions eachperpendicular to each other, and wherein each of the x, y, and zdimensions is at least 5 mm, with the proviso that if the metal oxideother than Al₂O₃ is CaO, then the glass further comprises a metal oxideother than Al₂O₃ or CaO at least a portion of which forms a distinctcrystalline phase when the glass is crystallized; and heat-treating atleast a portion of the glass particles such that at least a portion ofthe glass is converted to a glass-ceramic particles.
 25. A plurality ofabrasive particles having a specified nominal grade, wherein at least aportion of the abrasive particles is a plurality of abrasive particlescomprising a glass-ceramic, the glass-ceramic comprising at least 35percent by weight Al₂O₃, based on the total weight of the glass-ceramic,and a metal oxide other than Al₂O₃, wherein the glass-ceramic containsnot more than 10 percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅,SiO₂, TeO₂, and V₂O₅, based on the total weight of the glass-ceramic.26. A method for making abrasive particles, the method comprising:providing a plurality of particles having a specified nominal grade,wherein at least a portion of the particles is a plurality of particlescomprising an amorphous material, the amorphous material comprising atleast 35 percent by weight Al₂O₃, based on the total weight of theamorphous material of each particle of the portion, and a metal oxideother than Al₂O₃, wherein the amorphous material contains not more than10 percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂,and V₂O₅, based on the total weight of the amorphous material of eachparticle of the portion; and heat-treating the particles comprisingamorphous material such that at least a portion of the amorphousmaterial is converted to a glass-ceramic and such that a plurality ofabrasive particles having a specified nominal grade is provided, whereinat least a portion of the abrasive particles is a plurality of abrasiveparticles comprising the glass-ceramic.
 27. A method for making abrasiveparticles, the method comprising: heat-treating particles comprising anamorphous material such that at least a portion of the glass isconverted to a glass-ceramic, the amorphous material comprising at least35 percent by weight Al₂O₃, based on the total weight of the amorphousmaterial of each particle, and a metal oxide other than Al₂O₃, whereinthe amorphous material contains not more than 10 percent by weightcollectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on thetotal weight of the amorphous material of each particle; and grading theabrasive particles comprising the glass-ceramic to provide a pluralityof abrasive particles having a specified nominal grade, wherein at leasta portion of the plurality of abrasive particles is a plurality of theabrasive particles comprising the glass-ceramic.
 28. A method for makingabrasive particles, the method comprising: heat-treating amorphousmaterial such that at least a portion of the amorphous material isconverted to a glass-ceramic, the amorphous material comprising at least35 percent by weight Al₂O₃, based on the total weight of the amorphousmaterial, and a metal oxide other than Al₂O₃, wherein the amorphousmaterial contains not more than 10 percent by weight collectively As₂O₃,B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theamorphous material; crushing the glass-ceramic to provide abrasiveparticles comprising the glass-ceramic; and grading the abrasiveparticles comprising the glass-ceramic to provide a plurality ofabrasive particles having a specified nominal grade, wherein at least aportion of the plurality of abrasive particles is a plurality of theabrasive particles comprising the glass-ceramic.
 29. A method for makingabrasive particles, the method comprising: heat-treating ceramiccomprising an amorphous material such that at least a portion of theamorphous material is converted to a glass-ceramic, the amorphousmaterial comprising at least 35 percent by weight Al₂O₃, based on thetotal weight of the amorphous material, and a metal oxide other thanAl₂O₃, wherein the amorphous material contains not more than 10 percentby weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅,based on the total weight of the amorphous material; crushing theglass-ceramic to provide abrasive particles comprising theglass-ceramic; and grading the abrasive particles comprising theglass-ceramic to provide a plurality of abrasive particles having aspecified nominal grade, wherein at least a portion of the plurality ofabrasive particles is a plurality of the abrasive particles comprisingthe glass-ceramic.
 30. A method for making ceramic, the methodcomprising: combining (a) glass particles, the glass comprising at least35 percent by weight Al₂O₃, based on the total weight of the glass, anda metal oxide other than Al₂O₃, wherein the glass contains not more than10 percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂,and V₂O₅, based on the total weight of the glass, and (b) refractoryparticles relative to the glass particles, the glass having a T_(g);heating the glass particles above the T_(g) such that the glassparticles coalesce; and cooling the glass to provide the ceramic. 31.The method according to claim 30 wherein the refractory particles areselected from the group consisting of metal oxides, nitrides, carbides,and combinations thereof.
 32. A method for making glass-ceramic, themethod comprising: combining (a) glass particles, the glass comprisingat least 35 percent by weight Al₂O₃, based on the total weight of theglass, and metal oxide other than Al₂O₃, wherein the glass contains notmore than 10 percent by weight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅,SiO₂, TeO₂, and V₂O₅, based on the total weight of the glass, and (b)refractory particles relative to the glass particles, the glass having aT_(g); heating the glass particles above the T_(g) such that the glassparticles coalesce; cooling the glass to provide ceramic; andheat-treating the glass of the ceramic to provide the glass-ceramic. 33.The method according to claim 32 wherein the refractory particles areselected from the group consisting of metal oxides, nitrides, carbides,and combinations thereof.